Hi!
you should try to give your players around 50-70 minutes per week.
The chart in this link is a good indication:
(http://bbnews.cwsurf.de/cwjos/index.php?option=com_conten...)There are discussions about the perfect amount of minutes but I've always had one of the best average GS in my league when aiming for 50-70 minutes.
We have both said a lot of things that you are going to regret.