When can I change my player selection for each quarter?

You can change players for quarters that have not started yet, and you can change them as many times as you want.

You can also leave players unselected for quarters, but beware as if the quarter starts and you have an unselected player you can only score unmultiplied points for the players on that team during your turbo periods.

PRO TIP: make your changes quick though, since you could miss an epic turbo if you're in Pick Players too long.