Changing ovulation window?

Hi! I am fairly new to the app and just started TTC. I have been using the app for a few weeks now and at first it told me my ovulation window was last Thursday through Wednesday, my peak being on Monday. I took an ovulation prediction test 2 nights ago (it was positive) and logged it and my ovulation window changed to my peak being Friday, the day I took the opk, and the last day of my window being today. Has this happened to anyone else? Which one is correct?