Backup scheduler

I’d like to be able to run an automatic backup at regular intervals (for example every other day or every 3 days), rather than daily (too many) or on specific days of the week (not enough). The amount of days in a week is a prime number, so only daily or weekly give regular intervals. For example a selection of every Mo and Th gives alternating intervals of 3 and 4 days.

It does that. scroll down.