So I'm on winter break right now and i didn't decide on applying to MIT a few days ago. Its been a on/off thing. So i know the deadline is 1/1. Can i submit the app and then send the rec letters late?????
As long as the application is submitted on time, you can send additional materials for a few weeks. It takes several weeks for MIT to sort through all of the mail anyway, so having late recommendation letters isn't problematic (or unusual). Just try to submit them relatively close to the deadline.
You certainly can call the interviewer and explain that you've just decided to apply to MIT, and there's no harm in contacting him. However, it's unlikely that he'll be able to interview you, since the interview reports are due at MIT pretty soon.