Here's the skinny on Marine IFS as of right now. First off, I'm a Delta Grad (04-07) and am currently in IFS. There are two flight schools that are currently contracted to participate in the IFS program here in the Quantico area. One is bigger than the other and the bigger one is chocked full of all sorts of Lt's (meaning different Lt's from different graduating and on-coming TBS companies). It is chocked full and a little skewed right now because the flying weather up here has recently sucked and backed everyone up - to include myself. Those Bravo Co. Lt's that came to complete IFS before their class picked up were pushed into their TBS pickup date and are now flying on the weekends during TBS in order to complete IFS. This is to prevent interference with guys in my position during the week. So it is realigning it's just going to take a little time.
Enter Reasoning: For any incoming into Charlie or even Delta they might make you wait until after TBS just to make things smoother for a number of reasons - to many to type. So if you get thrown into Mike before classing up for your company just stick it out learn the ins and outs of TBS and hit the ground running cause you're going to do a lot.
So if you are contemplating whether to try to do IFS before or after TBS - I suggest after. It's a great way to wind down from the hiatus of Lovely Camp Barrett's daily operations, the hours are way better, and you are not operationally controlled by Mike Co., only administratively . You become the property of Aviation Training Branch on Mainside which is A LOT sweeter of a deal then Mike.
SEMPER FI