Don't put a time limit on it. It's kind of like taking a crap; when you're done, you just kinda know.
I am quite confused these days because most of the time I am at home and so i can practice a lot, but i had some problem.I don't know how to organize my practice... Say for example i am planning to practice for 6 hours this day. I can make them in 6 one-hour sessions or in 3 two-hour sessions or evem all in one 6-hours session!! The time of the sessions may vary, for example i can make a 1 two-hour session then 3 one-hour ones followed by a couple of 30 min...So, options are many and everything is possible. All I want to know is what is the best and most optimum time for a practice session so that you get most of it ??