A gallon of water weighs 8 lbs. If you held that gallon of water and stepped on the scale you’d weigh 8 lbs more. If you drank that gallon of water you’d weigh 8 lbs more.
So yes, all those numbers will be different.
Of course weight varies through the day and various stages of fasting and eating.
IMO, you are getting fixated on the scale. I like to be fixated on the process. The scale is just the downstream indicator of how I’m doing and if I take care of the fundamentals, the scale will follow. Execute the process. Celebrate a good fast. Celebrate a good eating window where you stay with proper food composition and calories.
Here is how I use the scale. I take my weight every morning near the same time. I log that weight in a spreadsheet. I don’t focus on that number at all. I have a 10 day running average. That’s what I look at. Am I coming down a little bit every day on that 10 day average? If so, I’m happy. It takes out the bumps and troughs you normally get with daily variations.