I haven't tracked it closely enough to know exactly when, but i know that just before I may not show a loss and after I will usually show a nice one. As far as weighing, I weigh-in once a week, but if it's TOM or I have eaten a lot of salt or had a splurge and expect not to show a loss, I'll sometimes skip a week. It's not cheating, I'm just being nice to myself and not getting upset over something that doesn't matter in the long run. There's no rules as to when or how often you weigh, or even if you weigh at all, for that matter!
Life's a journey, not a destination.
It's easier to stay on plan than to get back on plan.