48 minutes is the line for optimal training. Anything over that amount doesn't really negatively or positively affect your training that much. Your could have a player play 150 mins in a week and he would still get good training. What would suffer is his "Practice this Week" Practice this week is like form, it would impact how well he plays in games. I usually play my starters for both of my league games with no problems. They get 70-80 minutes most of the time and sometimes over. Anything above 90 mins and "Practice this week" will suffer. Playing 48 mins will get you a respectable Practice this week but it can go higher. I believe it goes up to proficient which I have reached from 70-80. I can't remember exactly...been awhile.