If you're marginal at the school you're applying to, yes it will hurt you. I definitely think that application date is the third most important factor in admissions. The vast majority of applicants apply after the new year, so technically it isn't late, but looking over LSN, late Dec vs. late Oct seems to often make the difference between a waitlist and an admit. If you've got high numbers for a school, you should still get in though. Head over to LSN, look at the school you want to go to, find those with your numbers and see how those who applied around the same time fared.