I gain and lose over the course of the day. If I'm up more than 2 pounds at night, then I know they'll be gone the next day unless I overate or had a really salty meal. I also know I'll wake up early and really need to pee.

I'm usually up about 1-2lbs at night vs the next morning though.
It doesn't matter what I gain during the day as long as it's from drinking a lot of water or eating a lot of low calorie, high fibre veggies. If it's from too much food or alcohol, then it takes a few days of being on plan for it to go way.