The largest amount of minutes you can give them in one week is 144, if you make them the starter, backup and reserve in league and Cup/scrimmage matches. You really shouldn't play them over 75 minutes (the preference around BB is 50-60 minutes a week for starters/backups) and if possible, play your trainees in scrimmages and single-position train them. To answer what I think was your first question, 48 minutes of training would be the same as getting 70 minutes in a week. Just get him +48 minutes of training and you should be fine.