Keeping temp in optimal range will help them grow faster. So if it's getting below the 64* F during night hours then I would consider adding a source of heat. However, if temps can get above 72 with lights on then I would let it get a little cooler to help keep the heat down when lights are on.
Enviroment is one of the most critical things in a grow. You can have the best nutrients, best lights and horrible results due to poor grow conditions.