I'm not sure how long it takes for interview letters to go out. That can range any where from now until April. I didn't interview at NYCOM until Jan. and I had my accomas application complete by mid June. I also know people who interviewed as late as April and were accepted. It's a big waiting game. After the interview, however, you usually hear within 2 weeks. I heard in 10 days exactly.
As far as preceptorships and clerkships, your clerkships are your third and forth year rotations. I believe preceptorships are similar to shadowing. I'm just a 1st year, so I don't know too much about that. I know that as a member of SOSA (student osteopathic surgical association), I can do a preceptorship this coming summer with a surgeon at Good Samaritan Hospital. I think it's for 2 weeks or something like that. Since we are medical students, we may actually be able to do somethings. I was told by several students who did the preceptorship last year that they were able to suture. There are several suturing workshops throughout the year from a couple different clubs.
I hope this helps!!