It depends if you are rooting them where the temperature will be at least 45 degrees. The cuttings will continue to develope roots as long as the rooting medium is at least that temperature or higher.

I take mine off the heat as soon as roots are developed. The space on the bottom heater is too valuable to use when not needed. I have a large cold frame I put them in for a few days or weeks before the open ground exposure. Al

What kind of heating pad are you using????

I am using a heating pad meant for back aches or sore necks! It works great!