it doesnt matter too much. i applied early in september and had a half dozen interviews set up by october. a lot of programs like the early applicants because they can schedule them for interviews early in the season (ie, november). a lot of people who wait may not be able to get an interview until january. by this time a lot of slots are filled and you dont have as much of a choice for interview dates. since i applied early i was able to have my choice of interview dates, which allowed me to geographically plan my interviews. it saved a ton of money in travel costs. for example, from chicago i went to indianapolis to columbus to cleveland and back to chicago. i didnt have to drive back and forth between chicago and other midwestern cities but rather knocked em all off in one road trip. i thought submitting on sept 1st (or whenever is the 1st day to submit) may show you to be a bit anal (which i am but i didnt want to show that!), so i submitted like sept 4th or something.
and you can also submit an incomplete app as well. dont submit something too bare, but if you have a LOR or 2, a personal statement, and all the application itself, i would go ahead and submit. but dont necessarily wait for all of your LOR's to be in, especially if you know you will, for example, be getting a letter from your sub-I attending in october or something like that.
