There is no way to guarantee a player gets 48 minutes in a game.
Lets assume the trainee is #1
PG:1/1/1
SG:2/2/2
SF:3/3/3
PF:4/4/4
C:5/5/5
Will give you 48+ if you use strictly follow depth chart(Obviously barring injury or foulout). This does guarantee 48+(once again barring an injury or foulout).
So to OP: THIS is the best way to ensure 48+
PG: 1/1/1
SG: 2/6/6
SF: 3/7/7
PF: 4/8/8
C: 5/9/9
THIS is the best way to maintain proper gameshape, maintain success and still give yourself a very high chance of 48+ minutes.
So in short: This post is pretty much useless, just wanted to be technical :)