It really is all throughout the season although submitting early puts you at an advantage where you don't have later interviews typically. I submitted late September, which is sort of later because I was waiting for my MCAT score and ended up having interview dates ranging from late October from the schools that acted really fast like PCOM-GA and LECOM-B all the way to April at PNWU where they won't let non- Pacific NW residents submit until December 1st.
It's all part of the long journey of med school admissions....