I weigh in on Saturday mornings as well. Excuse the TMI, but after the bathroom and before I eat is when I get the best results.
As others have mentioned, I find that I'm the lowest and (in my opinion) the most accurate during that time. Your weight will fluctuate even with a cup of water. It's always best to do your weigh-in in the mornings but if you also weigh in at the same time every week (even if it's at the end of the day), it'll still be relatively consistent week to week.
And yes, I also have weigh-in clothes!! I even take off my belt, watch, glasses, shoes, anything I can get away with. LOL