Time

In situations where keeping track of the passage of time is important, the DM determines the time a task requires. The DM might use a different time scale depending on the context of the situation at hand. In a dungeon environment, the adventurers' movement happens on a scale of minutes. It takes them about a minute to creep down a long hallway, another minute to check for traps on the door at the end of the hall, and a good ten minutes to search the chamber beyond for anything interesting or valuable.

In a city or wilderness, a scale of hours is often more appropriate. Adventurers eager to reach the lonely tower at the heart of the forest hurry across those fifteen miles in just under four hours' time.

For long journeys, a scale of days works best. Following the road from Baldur's Gate to Waterdeep, the adventurers spend four uneventful days before a goblin ambush interrupts their journey.

In combat and other fast-paced situations, the game relies on rounds, a 6-second span of time.

Speed

Every character and monster has a speed, which is the distance in feet that the character or monster can walk in 1 round. This number assumes short bursts of energetic movement in the midst of a life-threatening situation. The following rules determine how far a character or monster can move in a minute, an hour, or a day.

While traveling, a group of adventurers can move at a normal, fast, or slow pace, as shown on the Travel Pace table. The table states how far the party can move in a period of time and whether the pace has any effect. A fast pace makes characters less perceptive, while a slow pace makes it possible to sneak around and to search an area more carefully.

Forced March. The Travel Pace table assumes that characters travel for 8 hours in a day. They can push on beyond that limit, at the risk of exhaustion.

For each additional hour of travel beyond 8 hours, the characters cover the distance shown in the Hour column for their pace, and each character must make a Constitution saving throw at the end of the hour. The DC is 10 + 1 for each hour past 8 hours. On a failed saving throw, a character suffers one level of exhaustion.

Mounts and Vehicles. For short spans of time (up to an hour), many animals move much faster than humanoids. A mounted character can ride at a gallop for about an hour, covering twice the usual distance for a fast pace. If fresh mounts are available every 8 to 10 miles, characters can cover larger distances at this pace, but this is very rare except in densely populated areas.

Characters in wagons, carriages, or other land vehicles choose a pace as normal. Characters in a waterborne vessel are limited to the speed of the vessel, and they don't suffer penalties for a fast pace or gain benefits from a slow pace. Depending on the vessel and the size of the crew, ships might be able to travel for up to 24 hours per day.

Certain special mounts, such as a pegasus or griffon, or special vehicles, such as a  broom of flying, allow you to travel more swiftly.

Difficult Terrain

The travel speeds given in the Travel Pace table assume relatively simple terrain: roads, open plains, or clear dungeon corridors. But adventurers often face dense forests, deep swamps, rubble-filled ruins, steep mountains, and ice-covered ground--all considered difficult terrain.

You move at half speed in difficult terrain--moving 1 foot in difficult terrain costs 2 feet of speed--so you can cover only half the normal distance in a minute, an hour, or a day.

Special Types of Movement

Movement through dangerous dungeons or wilderness areas often involves more than simply walking. Adventurers might have to climb, crawl, swim, or jump to get to where they need to go.

Climbing, Swimming, and Crawling. Each foot of movement costs 1 extra foot (2 extra feet in difficult terrain) when you’re climbing, swimming, or crawling. You ignore this extra cost if you have a climbing speed and use it to climb or a swimming speed and use it to swim. At the DM’s option, climbing a slippery vertical surface or one with few handholds requires a successful Strength (Athletics) check. Similarly, gaining any distance in rough water might require a successful Strength (Athletics) check.

High Jump. You can leap vertically a number of feet equal to 3+ your strength modifier if you move at least 10 feet before the jump. If you don't move at least 10 feet, your jump height is halved. You make the jump as part of your move, and the jump costs your movement equal to the distance you jumped. You can extend your arms half your height above yourself during the jump. Thus, you can reach above you a distance equal to the height of the jump plus 1½ times your height. 

Long Jump. When you make a long jump, you can cover a number of feet up to your Strength score during your movement if you move at least 10 feet on foot immediately before the jump. When you make a standing long jump, you can leap only half that distance. Either way, each foot you clear on the jump costs a foot of movement.

Activity While Traveling

Stealth 

While traveling at a slow pace, the characters can move stealthily. As long as they’re not in the open, they can try to surprise or sneak by other creatures they encounter. 

Noticing Threats 

Use the passive Wisdom (Perception) scores of the characters to determine whether anyone in the group notices a hidden threat. The DM might decide that a threat can be noticed only by characters in a particular rank. For example, as the characters are exploring a maze of tunnels, the DM might decide that only those characters in the back rank have a chance to hear or spot a stealthy creature following the group, while characters in the front and middle ranks cannot. While traveling at a fast pace, characters take a –5 penalty to their passive Wisdom (Perception) scores to notice hidden threats.

Encountering Creatures. If the DM determines that the adventurers encounter other creatures while they’re traveling, it’s up to both groups to decide what happens next. Either group might decide to attack, initiate a conversation, run away, or wait to see what the other group does.

Surprising Foes. If the adventurers encounter a hostile creature or group, the DM determines whether the adventurers or their foes might be surprised when combat erupts.

Other Activities

Characters who turn their attention to other tasks as the group travels are not focused on watching for danger. These characters don’t contribute their passive Wisdom (Perception) scores to the group’s chance of noticing hidden threats. However, a character not watching for danger can do one of the following activities instead, or some other activity with the DM’s permission. 

Navigate. The character can try to prevent the group from becoming lost, making a Wisdom (Survival) check when the DM calls for it. (The Dungeon Master’s Guide has rules to determine whether the group gets lost.) 

Draw a Map. The character can draw a map that records the group’s progress and helps the characters get back on course if they get lost. No ability check is required. 

Track. A character can follow the tracks of another creature, making a Wisdom (Survival) check when the DM calls for it. (The Dungeon Master’s Guide has rules for tracking.) 

Forage. The character can keep an eye out for ready sources of food and water, making a Wisdom (Survival) check when the DM calls for it. (The Dungeon Master’s Guide has rules for foraging.) 

The Environment

Falling

A fall from a great height is one of the most common hazards facing an adventurer. At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall, or succeeds on an acrobatics check with a DC equal to 10 + 1 per 10 feet it fell. If a creature lands prone after the fall, they suffer max damage on the fall damage dice. In turn based combat, a creature that is pushed or falls off a ledge when it is not that creatures turn doesn't fall until the start of their next turn. If it is the creatures turn when they fall or are pushed off a ledge, the falling instead happens immediately. A creature instantly falls down 500 feet in a single round of combat.

Suffocating

A creature can hold their breath for a number of minutes equal to 1 + its constitution modifier (minimum of 30 seconds).

When a creature runs out of breath, or is choking, it can survive for a number of rounds equal to its constitution modifier (minimum of one round). At the start of its next turn, it drops to 0 hit points and is dying, and it can’t regain hit points or be stabilized until it can breathe again.

Vision and Light

The most fundamental tasks of adventuring--noticing danger, finding hidden objects, hitting an enemy in combat, and targeting a spell, to name just a few--rely heavily on a character's ability to see. Darkness and other effects that obscure vision can prove a significant hindrance.

A given area might be lightly or heavily obscured. In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.

Heavily Obscured. This occurs when an area -- such as darkness, opaque fog, or dense foliage -- blocks vision entirely. A creature effectively suffers from the blinded condition when trying to see something in that area.

The presence or absence of light in an environment creates categories of illumination: bright light, dim light, and darkness.

Bright Light. Lets most creatures see normally. Even gloomy days provide bright light, as do torches, lanterns, fires, and other sources of illumination within a specific radius.

Dim light, also called shadows, creates a lightly obscured area. An area of dim light is usually a boundary between a source of bright light, such as a torch, and surrounding darkness. The soft light of twilight and dawn also counts as dim light. A particularly brilliant full moon might bathe the land in dim light.

Darkness creates a heavily obscured area. Characters face darkness outdoors at night (even most moonlit nights), within the confines of an unlit dungeon or a subterranean vault, or in an area of magical darkness.

Blindsight

A creature with blindsight can perceive its surroundings without relying on sight, within a specific radius. Creatures without eyes, such as oozes, and creatures with echolocation or heightened senses, such as bats and true dragons, have this sense.

Darkvision

Many creatures in fantasy gaming worlds, especially those that dwell underground, have darkvision. Within a specified range, a creature with darkvision can see in darkness as if the darkness were dim light, so areas of darkness are only lightly obscured as far as that creature is concerned. However, the creature can't discern color in darkness, only shades of gray.

Truesight

A creature with truesight can, out to a specific range, see in normal and magical darkness, see invisible creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceives the original form of a shape changer or a creature that is transformed by magic.

Furthermore, the creature can see into the Ethereal Plane.

Food and Water 

Characters who don’t eat or drink suffer the effects of exhaustion. Exhaustion caused by lack of food or water can’t be removed until the character eats and drinks the full required amount. 

Food 

A character needs one pound of food per day and can make food last longer by subsisting on half rations. Eating half a pound of food in a day counts as half a day without food. A character can go without food for a number of days equal to 3 + his or her Constitution modifier (minimum 1). At the end of each day beyond that limit, a character automatically suffers one level of exhaustion. A normal day of eating resets the count of days without food to zero. 

Water

 A character needs one gallon of water per day, or two gallons per day if the weather is hot. A character who drinks only half that much water must succeed on a DC 15 Constitution saving throw or suffer one level of exhaustion at the end of the day. A character with access to even less water automatically suffers one level of exhaustion at the end of the day. If the character already has one or more levels of exhaustion, the character takes two levels in either case. 

Resting

Heroic though they might be, adventurers can't spend every hour of the day in the thick of exploration, social interaction, and combat. They need rest--time to sleep and eat, tend their wounds, refresh their minds and spirits for spellcasting, and brace themselves for further adventure.

Adventurers, as well as other creatures, can take short rests in the midst of a day and a long rest to end it.

Short Rest

A short rest is a period of downtime during which a character does nothing more strenuous than eating, drinking, reading, and tending to wounds.

A character can spend one or more Hit Dice at the end of a short rest, up to the character's maximum number of Hit Dice, which is equal to the character's level. For each Hit Die spent in this way, the player rolls the die and adds the character's Constitution modifier to it. The character regains hit points equal to the total (minimum of 0). The player can decide to spend an additional Hit Die after each roll. A character regains some spent Hit Dice upon finishing a long rest, as explained below.

Tending to Wounds

Players may also spend 10 minutes to roll hit dice and restore hit points, but get no other benefit of a short rest.

Long Rest

A long rest is a period of extended downtime, at least 8 hours long, during which a character sleeps for at least 6 hours and performs no more than 2 hours of light activity, such as reading, talking, eating, or standing watch. If the rest is interrupted by a period of strenuous activity - at least 1 hour of walking, fighting, casting spells, or similar adventuring activity - the characters must begin the rest again to gain any benefit from it.

At the end of a long rest, a character regains all lost hit points. The character also regains spent Hit Dice, up to a number of dice equal to the character's total number of them.

A character can't benefit from more than one long rest in a 24-hour period, and a character must have at least 1 hit point at the start of the rest to gain its benefits.

If your character goes over 24 hours without long resting, you must make a constitution save DC equal to 15 + the number of days since the last long rest. You must repeat this save every day until you take a long rest. If you fail the save, you gain one point of exhaustion.