My only issue is the fact that it's over a 24 hour period, I think over a 1-2 hour period before a reset would be far more reasonable. I can imagine marathoning one long session on a day off, and over the course of a full 10-15 hours easily averaging 1 missed dungeon every 3-5.

If it's to stop people from spamming queue there's no reason the period should be so damn long. Also what if you're queued with a half premade, and because of a consistent group of unready people everyone gets locked out. I've easily had groups of 5 or 6 people have to take several tries to get into an instant queue, because "Who dropped?" "Sorry that was me requeue" it's instant anyways so there's no loss to them.