I try to shoot a little a day. Practice sessions are short and focused. I think it is a mistake to shoot arrow after arrow if you are not working on something specific. Bad habits can be ingrained into your shooting very easily. Good shooting is all about proper form and when you get tired, good form begins to break down. Practice when you are fresh and strong and end the session when you get tired. Effective practice will transfer to better results in the field and on the 3D course. In other words, an individual's strength level, intensity, and focus should be considered relative to the length of practice sessions.
The end result of practice should be that you are not thinking about anything but the target (aiming) while executing the shot. Everything should be automatic.