Stupid question - January 1 ok to mail?

Very simple question here - most school say for the apps to be postmarked by January 1. That means it’s ok to send it on that day, isn’t it?

As opposed to December 31st. Though, I realize it’s risky, because you may miss the mail man if you can’t get it in on time, and then it would be January 2nd…

<p>An application cannot be postmarked on January 1st. The post office is closed,</p>