Tracking Time in a Dungeon
Dungeon modules may include instructions like
"Every 10 minutes, roll for a random encounter”
"characters who spend more than 5 minutes in this room must make a DC 10 constitution save against poison."
To clarify, these refer to time in the game world. There's no need to start a stopwatch for your players. It is useful to measure time outside of combat, though. Especially in a dungeon where it's dangerous to linger.
It also makes it easy easier to answer questions like "how long until it's dark out?" or "how long have they been gone now?"
Get a piece of graph paper or open Excel/Google Sheets.
Make a table with 12 hours that you can fill in and room for notes below.
Make notes of events like when torches were lit, when spells wear out, monster movements, when the party will need a long rest next, etc.
On paper, I do an X for 10 minutes and a single line for 5. I add a horizontal line to make an asterisk if there was a combat. Three X’s = half an hour. I also use vertical lines to track events so they don’t clutter up the time marks.
You don't need to record exact times or activities - it's fine if things are fuzzy. The goal is not to provide a log of what happened, it's just to estimate how much time has passed.
I try to abstract most actions into 5 or 10 minute intervals.
5 Minutes: A quick or simple task, or one that is aided by specialized tools or expertise. Most combats (1 round of combat is around 1 minute)
10 Minutes: A task that takes care or attention, or a task with complex steps. Examples:
Casually check a 20 x 20 area (1st edition)
Thoroughly search a 10 x 10 area (1st edition)
Move a distance equal to movement speed while mapping or checking for traps (1st edition)
Cast a ritual spell (5th edition)
But Why Add More Bookkeeping?
While it may be a little awkward at first, this soon becomes an unobtrusive part of play. It's actually easier than trying to track time by memory.
But more than that, time brings the dungeon to life. When time is part of play, you get events like torches sputtering out and mage armor wearing off that force players to strategize.
Monster movements become much easier to manage, as well. I like to write a rough schedule of when monsters will move barring interference. You could use it to move patrols or track progress in a fell ritual, for example.
For a simple 5-room delve, not necessary. But for a crawl? Indispensable.
Edit: you’re not crazy: I’ve edited this post for concision and to show what the graph looks like when it’s done on paper.