in a wo, the minutes are distributed on the line up
Starters: get 36 minutes
Backup: 10 minutes (5 when he already is starter)
Reserves: 2 minutes
You can combine it like you want, so a player who is 5* backup and reserve will get 60 minutes total.if he is also starter his 5 backup roles will count just 25 instead of 50 minutes, and he would get 71 minutes.
A player who isn't adssigned to any position will get zero minutes, even when you leave starters blank.