"Midnight on the 15th"

I am planning to go to a LAN event here, and knew that early registration would be doable thru the 15th, or so I thought. Now, when you hear the phrase “The deadline is midnight on the 15th”, don’t you automatically think that you have the entire 24 hours of the 15th to register in? That’s what I assumed, but the fools (almost Pittable, but not quite) who run the registration site don’t agree, but instead you had to register by the time the 14th ended-i.e that midnight is technically the 15th, but is that what most people assume? Yeah I snoozed and I losed (sic), but irksome nonetheless.

Midnight isn’t technically either day; it’s the dividing point between two days. That aside, if someone said “midnight on the 15th” I’d think one minute after 11:59PM on 10/15/07.