As SGT Cast stated you can PM SGT Avery for an extension as needed. Here are the requirements for completing OSUT:
-Completion of RCT training
-You must complete all 4 days in order
-You must be present during the training (yes I can tell when someone tries to AFK through a day)
-You must Complete OSUT in no shorter than 2 weeks but no longer than 45 days.
Therefor you could take each class with a different instructor and then take day 4 with your favorite, technically. It is recommended that you try and stay with one instructor so that you receive the best instruction and get to know a few of your fell members as well, rather than jumping from class to class.
Just be sure that when you are moving from class to class that you report in to the instructors thread every time you transfer to a different class. Doing Friday, Saturday you would be jumping between SGT Avery's and my class. Unfortunately our classes run on opposite weeks from the need to cancel classes in the past. So you would take his day 1 on 08AUG2015, my day 2 on 14AUG2015, his day 3 on 15AUG2015 then my day 4 on 21AUG2015, as long as you do not miss any days.