24 days is the max if I remember well, but too 5 days or 15+ days need 15 reds, so is the same 5 days or 20 in terms of reds....
About the change of schedule, as far as I know you recive a message in your inbox, so, sometimes one don't see these messages and is not easy to notice about.... in my case I can change always to a more late schedule, just when is +than 24 hours than the match one can change the match and put this before.