It all really depends on the size of the pump. I have a 90gpm pump and an 8500gallon pool.

Running a 15 amp motor 24 hours a day would be (1800watts x 24hrs x 30 days) = 1296000watt hours or 1296kwh. At 11 cents a kwh that's roughly $142 a month extra. You'll notice it. Even a two speed motor if you cut that amperage to 25% (3.5amps) you should see $35-40 difference. At todays prices I can't afford to filter that long. Not to mention that my pump would be rotating my pool like 13 times over per day if I ran it 10 hours a day. It doesn't need that.

Assuming it stays in line chemically, a few hours a day max.