It could be possible to get a letter in to ERAS in time. IMHO, it seems like a difficult thing to accomplish. I wouldn't make that a letter I was counting on (as in 1 out of 3 required from surg faculty), especially if you are having to depend on faculty who don't know you well. I would have the required number of letters before October, and I would hope for the October letter as "icing on the cake." Everyone is different though; I am cautious by nature.
The timing: In my experience this past year, it seemed like the deadline for all submitted information ranged from Nov 1 - Nov 15. (The dean's letter is submitted Nov 1.) If you could get the letter in before Nov 1, that would work.
Many schools give out interviews based on an incomplete application--before Nov 1. In my experience, most all of my interview invites came before Nov 1. My final letter was not uploaded until Oct 30, however, this was NOT a letter from a big name. I made sure to get my "big name" letters in as early as possible.
Does this make any sense?
Regardless of the LOR, you can always get a good educational experience from an away rotation, and it could still help you at that particular program.
Good luck.
