I would say that most schools still have plenty of open spots for January interviews. I had a late-Jan. interview and got in right away (and I had a 30 MCAT; so, make of that what you will). A friend and I interviewed at another school in mid-Feb., and he got in right off the bat (I got wait-listed with a good chance to get off the wait list but withdrew). When I came out post-acceptance to tour the school I now attend, interview season was still in full swing around mid to late March (and I know of at least two who were interviewing the day I came who end up being accepted). Don't stress it.