Intermittent Fasting schedule

I have lost 15 pounds by eating during an 8 hour window. There are days I shorten the window to accommodate my schedule and that is when I notice a bigger drop in weight. Is there something to that change in timing? Is it just the shortened eating window or is it because I have changed things up, or both? Specifically, will my body get used to an 8 hour window so I should plan regular changes to keep the weight dropping? Thanks!