More Volume = Better, As Long As Pressure Is Kept Low?

For the pumping veterans, we all know most report that going above a certain pressure (say 5 to 7) damages gains, but what about total volume of work? Have you noticed that staying in the tube too long, or doing too many sets, is counter productive in the same way that too much pressure is? What’s the sweet spot? An hour a day? Or the more = the better, as long as there are some scheduled rest days?