How long should each room in a dungeon take if the party didn't declare how long they spent there?

I'm running the party through a multi-day dungeon, and they're looking to long rest. Which is perfectly fine, but I remembered that you can't long rest more than once in a 24-hour period. I know how long it took for the party to get to the dungeon, but not how long they've spent in the interim.

Combat isn't a good indicator because its in-game passage of time is so short. They haven't spent any short rests in the dungeon yet, so I can't use that either. What should I do here? How do I go about determining how much time is spent per room for general exploration?

• Question is fine. Answer based on rules or citation or tested experience. – mxyzplk May 15 at 4:17
• Comments are not for extended discussion; this conversation has been moved to chat. – mxyzplk May 15 at 12:10

Mentioned in Chapter 8: Adventuring, the main rule to travel states that a fast speed is 400 feet per minute, a normal speed is 300 feet per minute, and a slow speed is 200 feet per minute. The default, therefore, should be 300 feet per minute, particularly when there's nothing interesting (featureless corridors, etc), and 200 feet per minute when there's any particular need to be cautious (e.g. stealthy), or if they're actually looking for something.

A more detailed blog post (does not quote official material, but looks legit) suggests 5 minutes for each trap/lock if proficient and equipped, 10 minutes otherwise, up to 20 minutes for secret doors/passageways (with an Investigation (Intelligence) check to reduce time), and a general guideline of not more than 10 minutes per room for activities, unless the players choose to exhaustively search a room (20 minutes). I can't seem to find rules for these actions right now, but I remember using similar guidelines in many groups both as players and as DM.

You might want to keep track of seemingly mundane details to help calculate time. Did they spend 30 minutes deciding if they wanted mutton or pork? Did they decide to spend an hour reading books in a library? Not every room is going to go at full speed, and you might even automatically add in some time-wasters to help pad out the time if your players don't do much on their own. Add a lot of locked doors, and traps, and secret passageways, and treasure boxes. These all take time, and if designed well, will take more in-game time than real time.

The rules are a decent start to tell how much time has passed, but you should be prepared to arbitrate various random activities that do consume a lot of time but are not covered by the rules. I had one DM that even advanced time if we took too long deciding what to do in a room, as if our own indecisiveness was reflected in our characters. Be creative, and you can easily find places to realistically add many wasted hours in a day to help your players reach legitimate Long Rest points (preferably near the end of a game session).

There are no specific rules for these things in 5th edition.

However, pretty much exactly this issue was addressed in earlier editions of Dungeons & Dragons, like the Basic Edition from 1981. The method used there is to divide all periods of time into average chunks of 10 minutes each. (Somewhat unhelpfully named "turns".)

An encounter is assumed to take 10 minutes, which includes any pre-combat planning among the PCs when they spot enemies without being noticed, looting the fallen, and tending to their own injured.

Searching a room also takes 10 minutes, unless the room is very big and it might take 20 or 30 minutes.

The durations of torches and other light sources can also be divided into 10 minute chunks. In these earlier editions, most spell durations also came in multiples of 10 minutes. Random encounter rolls would also be made every 10 minutes.

The idea here is not to be precise or realistic, but to track time at a degree of abstraction that is easy to use during actual play. With this method, you don't really need to count the minutes or rounds of anything. You simply have all the timers advance by one "exploration turn" and make a random encounter check for every room the players search or every encounter that they have.

Using this method, a day has 144 turns, 48 of which would be taking a long rest, and 96 the rest of the day.