Try to hold the water in for 5 minutes, and then expel completely, you should get most of the large fecal masses out of the bowel. Not everyone can take one quart then again others could take more. It is an individual thing. If it hurts when you don't want it to, something is wrong and it's time to stop. Lie in a comfortable position so that there is no pressure on the bowel and breathe in slowly.
Relaxation is the key.
Under no circumstances should you try to forcibly expel the enema fluid from the bowel as you may try if you were constipated. Allow the enema and nature to take its course. Not a good idea to try doing an enema to a timetable. 7.30pm sit down and eat 3 course meal. I don't think so.