In order to best ensure that the game engine plays the lineup you set, you should fill in all fifteen slots (starter, backup, and reserve for each position). You can fill in the same player in more than one slot, as long as he's not a starter more than once.
Thus, the best tactic to get as many minutes as possible for a single player is to place him as start, backup, AND reserve for his position, and use the Strictly Follow Depth Chart option for substitutions. This does NOT guarantee 48 minutes, as foul problems, extremely low stamina, or an injury may lead to the player being subbed out, and the coach putting in a random stiff from the bench.
Conceptually, it is possible to only dress 5 players and have each as Starter/Backup/Reserve at a given position. However, you are likely to lose at least some time to Lucky Fan.