My 11b 14-week OSUT starts(ship late August) on 9-05-11.Wondering if I will be back before Christmas exodus?

I have already looked at it on the calender and I am borderline, but should be good. Reason I am wondering is because I must be back in school by January so I can contract ROTC and be a SMP cadet. Since time is critical, was mainly wondering if there is anything random that would hold me over late, even if it's a couple of days. For example reception lasting longer than planned, a day off for Thanksgiving or whatever. (ship 8-22, official start date of basic says 9-5 in contract)