Make sure the heatpad doesn't get too hot...I had one (Exo-Terra 'Heat Wave') that went into the 100s. Right now I'm on a 75W light that's keeping it a comfy 84. Mine is in a 25-gallon, so the lamp's a good foot above the substrate.
I just turn it on in the morning, and off when I go to sleep. When I move him out of my bedroom eventually, I may or may not keep it on all night, depends on how my mother feels about that.