In this case, the coach will simply pick somebody who isn't in the depth chart, even if you put strictly follow depth chart.
...Basically, you have to avoid playing the same player as a starter twice to get that result....
...every now and then you'll get a week where 1 person doesn't quite get the minutes needed but it's not a huge problem.
...Also, if you want to increase your chances of having your player play 48 minutes you should play a slow offense in your friendlies...
In the case you're talking about.