there is really no way to determine how much time your starters and back-ups get. if the players who are playing the same position are similar in skill then you can expect them to get a similar amount of minutes, but if the skill difference is great then you will have a hard time getting the benched player out on the court. the only way you can guarantee that a certain player gets the full 48 minutes for the week would be to set your tactics at "coach strictly follows depth chart" and only put 1 player in that position while removing the other players from the line-up. that's what i've had to do for my center trainee. he's not as good as my starting center who starts for a national team so i have to make sure he gets his minutes. but after a few pops the minutes should start to level out.