In order to err on the safe side. I always cut the pumps 15 minutes after an hour...60 on 15 off. this allows the pump and rez to cool. On the other hand. If you find that the floor is too cold, you may want to leave pump running in order to keep you rez temps warm enough. what you need is to run the system and take rez temp measurements after pump runs for an hour.
if temps are above 70 degrees turn off 15 minutes check temps, and start pump again. monitor rez temps for another hour. If temps are not above 70 degrees. keep pump running and monitor hourly, until you determine stability. It is also a good idea to turn off pumpo every couple hours in order to let debris clear from pump inlets. goodluck, and I hope this helps.

If you cannot keep water up in the 60's, then build a 2" high plywood subfloor, the little bit of airspace between the warm rez and the cold floor will balance your rez temps somewhat