Yeah if you're into math, I think it's on a sort of logarithmic scale. In other words the farther down you get from 48 minutes, the more impact it has. If you have a dude at 47 minutes after Saturday's game, just play them as a backup next game so they hopefully get 5-15 more minutes. Unless you're 1-position training 3 different players, then 47 minutes should be fine.