If indoors then the closer you can keep your lights, without inducing burning, they might not grow very tall. In my history of cultivation I have vegged plants for 3 weeks from clone (outside the propagator) under 600W hps using an adjustawing shade and they didn't stop vertical growth until over 5'. But I now use an air cooled shade and am able to keep the lighting 50% closer which limits the 'stretch' when the lights get turned down.

Luck!