Army security clearance questions?

I signed up for the army reserves awhile ago, and am awaiting for my DEP to be over so I may go to meps one more time to get my second sworn in and then go to BCT and AIT, and I was wondering when and how long will my secret security clearance take, as my mos requires me to have one, and what would happen if I were to not get the security clearance, would it mean I'd have to be recled?