I've always been really conflicted about the night time watch system. On the one hand, it's a good way for a DM to mess the party up. But the reality is that unless they are on a time-sensitive mission, most parties then just have a rest day to get their spells etc back, so all it does is slow things down.
Nowadays, I ask that the players set up a standard watch rota at the start, and then generally let them have their rest unless there's a good reason in the storyline not to. But then I mostly play 3.5 rather than 5th Edition - unlike 5th, with it's Long Rest mechanic, 3.5 is more about spells returning at dawn but only if you've had a full night's sleep (that's the simplified version, of course...)