I have 11 players 5 of them normally play the entire game. The other 6 must be on the roster playing a full quarter in each half.  Can I sub in any of the minimum play players for one of the 5 that have already met the required play time 2nd or 4th qt ? 

thanks

Your only required to mark down 1 quarter in each half for each player. So if you get to the 4th quarter and 1 kid has already played his 2 quarters that were marked and another has as well that normally plays the whole game and you wanted to play the other kid who doesn't play more than 2 quarters typically then you could play him in the 4th, but as far as pullings kids in and out of an ongoing quarter no it's not allowed.