The best thing is to play how much you can...
For a human body who doesn't know the poker world, works for 8-10hours per day....so you can also make that in poker too....but i guess sometimes you can try more, other times ...you will try little bit.
My sessions are like this....i register in "n" mtts and sngs and IF THERE IS something interesting still in this session i will try to register also in more....but i don't really like to make 2 sessions one after the other....becoming boring and also your senses becomes really atenuated....
IF you want to be profitable, you must imput the "positive line" into your poker session..What means that? Is just all you do with the time to be prepaired 100% for poker and have the attitude necesarry being to win the best