The very high level view of “1-1 time keeping” is that when time passes in the real world, the same amount of time should pass in the game world also. Here’s a better explanation. The origin is (if you squint sufficiently) in the original Gygax AD&D rules, but the real “this is the way” push for it was from Jeffro Johnson and the BROSR people: some history here. Alternatively, “West Marches”-style campaign play does not demand exact 1-1 time, but does want time to progress between sessions.
And I apologize if you’ve never seen all these references before, this is a decade of theory with its own lingo, etc.. Keep reading anyway,
These are some worked through examples for idea exploration reasons. As with many things, it is not necessarily finished but not necessarily not finished either.
TL;DR
The reasons you would use 1-1 time as a DM are:
to coordinate DMing many different players / groups over time in the same campaign world,
to create time pressure on players so they show up whenever a session is being played.
The major outcomes of using 1-1 time are:
sometimes PCs will not be available to players because their characters are “in the future”; they can use alternate PCs in this case
sometimes - very rarely if managed properly - places will not be available to PCs to visit / interact with. Stricter DMs believe this should never happen.
because things are always happening, you should resolve things happening between sessions “off stage” via emails or Discord
Single Party Examples
These are less interesting, but set the baseline.
Example 1 - Single Party, in Town, little game time passes
They play one session on January 1. It starts game time June 1 and ends the same day.
Two weeks pass and they play again on January 15. The game time is now June 15.
14 days passed in the real world, and they automatically pass in the game world too. This is the only “surprising” change for Single Party examples, everything else will work the way you’d normally expect.
Example 2 - Single Party, In Dungeon, little game time passes
They play one session on January 1. It starts game time June 1 and ends the same day. The party is still in the dungeon.
Two weeks pass and they play again on January 15. The game time is still June 1.
1-1 time assumes that players should not be staying in dungeons overnight, and this should be highly discouraged. If there was another party, the dungeon could be mysteriously not enterable until the first party resolves its situation.
My understanding of the BROSR people is: this scenario should not be allowed - they leave, one way or another. The actual reason why can be worked out on Discord / email, or can just be by DM decree.
Example 3 - Single Party, in Town, a lot of game time passes
They play one session on January 1. It starts game time June 1 and they do training and research for 4 weeks, and so ends July 1.
Two weeks pass and they play again on January 15. The game time is now July 1.
Nominally we’d expect the game time to be June 15, but since everyone is in the future, we can just jump the clock ahead to then. (I’m not sure if the stricter versions of 1-1 time allow for this, but it would be pretty boring if your PCs are taking a Slowboat to Alpha Centauri).
Multiple Party / Open Table Examples
This is where it gets more interesting / relevant.
Two Parties - in Town
Party A plays on January 1. The game time is June 1 and it ends the same day.
Party B plays on January 8. The game time is June 8 and it ends the same time. Although Party A is not playing, they are nominally on June 8 also.
Party A plays again on January 15. The game time is June 15, and nominally Party B is June 15 also.
Straight forward enough!
Two Parties, one (in a) Dungeon
Party A plays on January 1. The game time is June 1 and it ends the same day but the party remains in the dungeon.
Party B plays on January 8. The game time is June 8. If they go looking for the dungeon, they cannot find it nor can they find party A.
Party A plays on January 15. The game time is June 1 (nominally the past). When they leave the dungeon, they find suddenly a need for rest & relaxation and the time jumps ahead to June 15. Party A and Party B have reached time parity.
Note that 1-1 (again) strongly doesn’t like players jumping out of time by being in a dungeon. Ideally, they would leave that session, or a session with Party A would be held as soon as possible to resolve the situation, or maybe at some point the DM will just say “Party A left the Dungeon”.
A party in a dungeon between sessions needs to be resolved ASAP to stop time management problems.
Two Parties, a lot of time passes
Party A plays one session on January 1. It starts game time June 1 and they do training and research for 4 weeks, and so ends game time July 1.
Party B plays on January 7. The game time is June 7. Let’s say they finish the same day.
The players from Party A want to play again on January 14, which would be June 14 game time. They cannot use the Party A characters - they are not available because June 14 is before July 1. They can roll up alternative characters if they want to play today.