I depends on what you’re hoping to get out of it. For example, I find my lowest weight is first thing in the morning, after using the bathroom but before eating or drinking anything. This is the number I go by for my weight. If I want to torture myself, I’ll get on the scale at night, fully clothed, before I go to bed. The hope there is that I will see the number, remember it the next day, and make better food choices.