I weigh first thing in the morning (not every morning but always first thing when I do weigh) and completely naked, after a pee
But no matter when you choose to weigh, the most important thing is consistency. If you choose mornings, for example, stick to that. Or if you weigh before bed, stick to that. Your weight can fluctuate quite a bit throughout the day and you may find that you weigh more at night than you do in the morning due to food intake, water retention, etc. You'll find those 3 pounds lost to be more accurate if you compare apples to apples instead of oranges.