I agree, but I would keep the QT running all the time. I have mine running at all times so I dont have to keep setting it up and tearing it down.
I started mine by doing a waterchange on my main display and added the 12 gallons the my QT tank. Ity was running and ready for fish immediatly.  It is also a good ide to have a air stone int he QT tank to help keep the PH balanced.