The amount of minutes you have assigned to individual players does not determine how high their overall rating will be be. In order for a player to reach 700 in D3 he needs to have lots of potential. Most people use 20-25 minutes for their offense they run, and another 20-25 minutes for the defense they run. This amount will get your players to an A or A+ in IQ during their senior year as long as they have enough WE. If you need more advice I would recommend getting a mentor or reading
this guide if you haven't already.