Heat pump cools house to 72 degree all day until 7 oclock in the evening. I will turn system off for a couple minutes then back on.it works good for several hours then the same thing happens

Have you inspected it when this happens? Is it frosting over blocking the vents? Have you had it serviced lately?

The heat pump does this in heating and cooling and once I turn it off for a half hour then back on it works fine for 8-10 hours. Could it be a compressor internal overload kicking in and out?

That is possible and also if it is low on freon you can get some of the same symptoms.