a controller that turns your pump on and off is the most efficient way to achieve this.
next is a valve that opens/closes to achieve
then a controlled leak.
if you shut off the pump, vac levels will change over time. which slows you down. other than that it doesn’t really hurt much. keeping the terps and losing the solvent is a balancing act between time/temp/vac level. given that input material makes a huge difference in exactly where that balance lies, you’re going to have to feel around a little bit. read, experiment, evaluate. repeat.