joes87 - when you say mid-january, when are you assuming he starts throwing again (or asked differently, are you assuming a 75 shut down period?).
phillyinNJ - No expert here, but part of shutting down is having a plan to ramp back up. I know there have been some threads that discuss this but not exactly sure what to search. I do know there is a progression starting with short toss, moving to longer toss, adding some flat ground throwing and then finally throwing from the mound. That is overly simplistic, but once you find a good program that fits, it should dictate the amount of time to get back to 100%. As far as shut down period, 90 days is good and necessary if the kid had a heavy pitching season. The lighter the load, the shorter the shutdown needs to be. So, you have two time periods that you need to establish (shutdown, ramp up) at which point you can find your answer.