For bulking, as little time as possible. It's better to go at a lower weight and do sets as frequently as possible (10 - 20, optimally). This increases muscle size, more than strength - but with bulking, that's the idea.
Your creatine phosphate levels return back to 99% normal within 90 seconds. So, you might shoot for 90 seconds and each workout try and shave a few seconds off till you have a 1 minute rest period.
