In the app, click on the mouse head, then "get fast passes." Click on the existing one that you want to change, click modify, then select the people, then continue. It pulls up availability. At the top, it says "search by time" and there are multiple times listed: 1:30PM, 2:00PM, etc. Scroll left and right, and choose the time you want to search near. Wait a sec, and new availability pops up closest to that time. If you don't see one you like, choose another time under the "search by time" bar. Lather, rinse, and repeat until you find one you want.