I think you're hoping that other people have seats on hold and that those holds are going to expire, so if you call right after midnight you can snag some of these.

That's very unlikely to happen. Some seats may open up, but it will be much closer to the departure date. Assuming you have something on hold now, book it and then keep monitoring availability from time to time (more frequently as you get closer to your departure date). If you can set up an ExpertFlyer alert for the dates you want, even better.