In this business, sometimes you've really gotta know your time zones. When you come down to the wire on a paper, sometimes it really matters whether it's East Coast, West Coast, or (as in my unfortunate case this evening), Central Europe. At some point, the deadline has really, truly passed, and the submission site shuts down, and the computer won't take your paper any more.
It's important to know exactly when that is, which is why computer science conferences generally choose 11:59pm or 12:01am, avoiding the date ambiguity of midnight, and always specify the time zone---usually somewhere in the US or Europe, but occasionally as far West as American Samoa (because computer people love to find extreme edge cases). A later deadline doesn't necessarily help, of course, because it's just encouraging you to stay up later at night if you aren't yet done.
Properly, this shouldn't matter. We should all be good little boys and girls and get things in before the last minute. Nobody should ever have to wonder which midnight it is, but we do have to sometimes: maybe there's another deadline first, or maybe you figure out something new as you're editing a paper and you have to make lots of extra changes to fix it, or maybe it's ongoing work and you're still adding new material, or maybe you're just crap at deadlines. I honestly don't think the last actually pertains very often to last-minute submissions: I think more often it's just the combination of perfectionism, triage, and shrinking margins of error.
When I was an undergraduate, I had a theory about deadlines that worked pretty well for me. I held that taking a semester of classes was like surfing on a wave: you start out up at the front on top, and every time you let anything slip, you slide a little bit further back on the wave. If you slide far enough back, you're in danger of falling off (missing assignment deadlines), and you get really stressed and can't do anything that you want to because if you miss one step, you fall off the wave. But you're always doing the same amount of work: it's just that when you're farther from the deadline you've got more options for moving it around and doing the stuff that fits better with your mood/desires/headspace at the moment. Oh, and having less stress. So every semester I'd start off doing my assignments the moment that I got them, and slowly slip back towards the deadlines as the work piled up. Then the semester would end, there would be no homework assignments over break, and I'd be reset up on the top of the wave again at the beginning of the next semester. Only now, as a working professional, there are no semester ends for me any more.
Technically, I'm already 10 days past the deadline on this submission, but first the conference extended the deadline by seven days (which is not unusual), and then a note went around that the submission site would actually continue staying open for three days beyond. And so I embraced work-life balance for the weekend: played with my daughter while my wife dealt with her own last-minute paper crisis, went up to Maine to visit my parents, got a couple good nights' sleep. Today I spent most of the day on an ongoing project that's actually billable, as opposed to this paper which is more directed at future work and foundational principles. No problem: I knew I had only about three hours of work to go to finish up the paper, and I came in right on time, even a little bit early (though not as early as my ambition, of course).
And the site was closed.
You see, I'd read "CET" and thought "CST". CET is Central European Time, where Italy and Hungary and Germany are. CST is Central Standard Time, and has Iowa and Texas, and Chicago. Seven hours difference this time of year, most times of year in fact, except for a brief transient when Daylight Savings is different in Europe and the US (God only knows why). And so that's why my paper is still listed as "abstract only" at this moment.
I'm not sorry, because it's ended up as a damned good paper, full of pretty pictures too, so if it doesn't go here, it will find another good venue. And hopefully the program chairs will have mercy on me and allow my paper to proceed into review in any case, because I'd really prefer it to have a chance to go where I intended---that's an audience that I like a lot and think will really appreciate the ideas. But for now, I'm tumbled off my wave and hoping to avoid the same mistake on the next one.