No it's not. They've got 5-6 players for 2 positions (for example PF and C) and they rotate them from game to game, to have this 48 minutes.
You can do both - the risk of rotating is that you might get 55-41 split in mins over 2 players in 2 games.. the risk to setting no backs up is foul trouble or injury.
I actually prefer the no back up option.