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The phrase "24-7" is a common term for "all the time", referring to the 24 hours in a day, 7 days in a week. Early in one of the games I'm playing in one of the other players made an in-character comment of: "38-6". At the time we thought it was hilarious and allowed it to become cannon for our world. We now have a 38 hour day where characters only long rest once per day. We also have a 6 day week, though I don't think this poses as many issues.

I was recently running a session where one of the side effects of this came up. The players spent all night on a heist mission, finishing at dawn. They then took a long rest and got up at mid-day. I ruled they could do this since there was 10 hours between dawn and noon in this world. However I am wary of exploits going forward.

What are the consequences of having more than 24 hours in a day?

Other than the obvious resting issues that I encountered, I also remembered there are some spells/abilities that are once/24 hours rather than once/day. I'm interested to know if there are any problems with continuing to allow this in our game.

We have a large party of level 4-5 characters and play a mostly story driven game with rotating DMs. None of the players are power gamers that are likely to deliberately exploit issues but we may abuse it by accident.

(Assuming you are not necessarily jamming more encounters into the day just because it is longer:)

Certain spells have a duration in hours that are expected to last anywhere from a good chunk of the adventuring day to 'an entire dungeon crawl'- spells like aid, higher level versions of hex and hunter's mark, mage armor, and most of the other results that turn up if you search for "hour" in spell durations & effect text.

My first thought upon hearing a 38 hour day is that if longer days mean your encounters have more time between them, there's a higher likelihood that these spells will fall off and cause casters dependent on them to have to spend more slots per day to maintain them. Mage armor lasts half the time you're not resting in a 24 hour sleep cycle world, but in a 38 hour sleep cycle world that goes down to ~27% of the time you're not resting.

To put it more broadly, 38 hour days indirectly nerfs any encounter-assisting spells or abilities that have a 'long' duration- I'd say anything 1 hour or up- assuming it has a limit on how many times it can be used per long rest/day.

The other effect I can think of is that there's more room for short rests in the day, assuming they remain at 1 hour. This won't necessarily help health recovery- you're still throttled by available hit dice- but if the party can fit in more short rests, that means their per-short-rest abilities are available for more encounters each day.

If most resource-draining encounters take place within an 8-16 hour timespan, as with 24 hour days, these concerns are more or less minimized. If you're now spreading things out over your 30 hours of wakefulness, however, you might run into odd things that need accounting for such as the above.

A history of the Hour

We all know there are 24 hours in a day because that's how the Sumerians divided up the day. And we know that a day is 60 minutes of 60 seconds (again Sumerians).

And some of us know that one second is "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (at a temperature of 0 K) - this we do not get from the Sumerians because they didn't know about "radiation", "hyperfine levels", "caeseam-133" and "0 K".

What they did know is that when the sun comes up, that's the start of hour 1 and when the sun goes down, that's the end of hour 12 and the start of hour 13 and when the sun comes up again, that's the end of hour 24. Now we (and the Sumerians) know that daytime in summer is longer than daytime in winter and so, logically, a summer daytime hour is longer than a winter one and vice-versa for nighttime hours.

This makes perfect sense for a society that measures its hours by the sun and operates at the speed of a person on foot (or horseback). It doesn't work so well for a society that measures its hours by atomic clocks and uses them to coordinate a global society.

So we changed what the arbitrary, human-made hour was defined as.

This change started when we began fiddling around with clocks. Because clocks run on springs and cogs and caeseam-133 and not on dawn and dusk we redefined the hour. Later, when trains came along and it became necessary for people a long way apart to agree on a common 'time' we invented time zones. NASA's Mars missions divide the Martian day (a 'Sol' = 24 hours, 39 minutes, and 35.244 seconds) into 24 Martian hours and their scientists and engineers adopt the rhythms of a planet 225 million km away (on average). Later still, Einstein worked out that how long an hour was was all relative anyway because hours and metres are actually interchangeable.

The point is: an hour is a human-made invention - it is as real as 'Santa Claus', or 'justice', or 'love'. That is, its real to us but not to the universe.

Consequence of changing it

None.

Seriously, none.

For a start, you haven't even told us if your fantasy world's day is half as long or twice as long as Earth's. Or, for that matter, if it even has a day/night cycle. Or, if it does have days and nights if they are any way cyclic- my campaign world is the severed hand of a long-dead god orbited by what most people believe is the god's glowing eye (they're wrong - the reality is much, much worse) and the thumb and fingers play merry havoc with things like "dawn" and "dusk": some days have 1 of each and some can have up to 5.

Outside of combat, timekeeping is not very important. Sure some spells and effects last 1 minute, 10 minutes, or 1 hour or 8 hours or 24 hours but if you just substitute 1 encounter, 1 while, 1 longer while, about 1/3 of a day and 1 day nothing's going to break that you can't fix with a ruling.

The types of issues that you suggest might be issues are simply not issues unless you choose to make them such.

You get 1 long rest rest per day - there is nothing to suggest that this downtime corresponds with day or night. Humans are awake for roughly 2/3 of the day and while this generally coincides with daytime hours this is hardly universal (e.g. shift workers, teenagers, babies and their parents). If you miss a night's sleep you sleep might sleep away the morning but no one would sleep through till dusk.

From a mechanical standpoint, you only get long rests when you need them - do you track long rests during 3 months of downtime? Of course not, you assume the PCs go through a normal sleep-wake cycle for each of those days. The mechanical impact of a long rest is to reset damage and spellcasting - this is only worth worrying about if there has been damage and spellcasting. mechnically you should be taking long rests after 4-6 encounters - too few and combat becomse too easy, too many and it becomes too hard - allow your PCs to rest when the pace dictates and don't sweat how long it all takes.