There has been some debate recently about 'how long rests are exactly' and 'when do they end'.
In part the confusion is created because instead of just saying a short rest is 1 hour and a long rest 8 hours the PHB says at least 1 hour and at least 8 hours.
Now, the smart ones among you will realise that the writers put in the 'at least' phrase to prevent pedants from denying the benefits of the rest to those who rest for more than 1/8 hours on the (obviously spurious) grounds that "It says 8 hours, 8 hours and 10 minutes is not 8 hours, therefore you don't get the benefits because you haven't rested for exactly 8 hours!" The trouble is that pedants always find a way....
But the answer, the RAW answer, is there!
We also know that Spellcasting slots/Rages/loads of other features are refreshed after a long rest.
The key point is that you only get these things refreshed at the end of a long rest. Therefore, if you have just had these things refreshed, that long rest must have ended!
There is no getting round it. If the long rest had not ended then you would not have gained the benefits. You did gain the benefits, therefore the rest must have ended!
There is an exactly similar (watch out for those pedants!) RAW answer to when a short rest ends:-
...and all the other short rest resources, like Pact Magic/Ki points/Superiority Dice/etc. If you have rested for at least 1 hour, and the DM tells you that you get the benefits of a short rest, then that rest must have ended! If it had not definitely ended, you could not have gained its benefits.
But what about the 'at least' part? Doesn't that mean that rests can be longer than 1/8 hours?
Well, yes and no.
First, the 'yes' part. The DM can certainly say that you guys have been resting for, say, 12 hours, so give yourselves the benefits of a long rest. There is nothing wrong with that.
But for the 'no' part:-
....if you have been resting/avoiding strenuous activity for 8 hours, and you ask the DM, "Have we rested long enough to get our hit points/spell slots back yet?", the answer is an unequivocal 'yes!' Why would your DM deny you the benefits?
Because he thinks you might be resting some more? The problem with that is that the players are resting in order to gain the benefits, and will damn well keep resting until they do! They will only start doing something else when they get their hit points/slots etc. back!
What about an 8 hour rest followed immediately by a 1 hour rest? Isn't that just one 9 hour rest?
It is utterly pointless to have a short rest straight after a long rest, because a long rest has already given you all the benefits that a short rest would. You rest to gain the benefits; a short rest lets you spend hit dice to heal, but you already have all your hit points from the long rest. A short rest lets you get your Pact Magic slots/Superiority Dice/Ki points and so on back, but the long rest you just had already gave you all of those things.
What about if I have just got the benefits of a long rest (indicating that the long rest is definitely over), then I cast some spells/use other short rest resources/take damage? What if that spending of resources only takes a minute? Or 6 seconds?
In that case, you can benefit from a short rest! We know for a fact that the previous long rest is over, because if it wasn't over then you could not have gained those long rest benefits. Therefore, any time spent resting after that long rest must be nothing to do with that already expired long rest.
Any questions?
I have a question. Is this actually an argument that happens? Do people actually argue over when a rest ends, instead of just saying "you have taken a long rest"? If so, why?