Within 1-60 days you have to get a signed i 20 with start date that's in upcoming 90 days..
This includes the day you get your new I20, don't aim for 60 days, any issues you loose status. Aim for 45 days. Give 15 days for delays of whatever.

You classes have to start within 90 days of your signed I20. Again dont aim for 90. This will depend on when the actual semester starts at the school.
Beyond 91 days you will loose F1 status.