If you weigh yourself on an evening, your really setting yourself up for mental focus problems...Not saying deffo will but its more than likely.
Circle usually goes, weigh in on night, youve gained your down. Weigh next day your still up from last proper weigh in.. your down, you think eat less...you eat less may be lower number that evening for not eating, next morning you weigh your the same.. your not happy you eat less.
This is when you start to get into trouble, mentally you will continue to cut cals because of the 'number' you see.
(Btw not saying this is you lol)
I got into this situation last year its not a nice place to be, why im now saying do not look at scales more than once a week cuz it causes more harm to you than good.
To answer your question i could gain upto 6lb in a day. Now i dont know as i dont look.