I had a friend a couple of years ago who waited until the last day, and the system crashed and he had to submit a hand written copy by mail by midnight on that day. Hasn't happened in the last few years that I know of, but I always submit mine at least 3 days out just in case. After all, you charge on a credit card, which means they won't get their money for a few days anyway and your bill won't come due till next month.