Roughly four hours a day, ideally split into a couple of different segments at different times of day.
The speed should be set to the lowest speed where the skimmers work well and if you have a heater, the heater is happy with.
Is this a general rule of thumb? I'm also interested in a schedule for my setup - I have a Pentair Variable Speed IntelliFlow where max RPM is 3450. Builder told me 8-10hours on 2200RPM-ish...