One interesting thing that could be in a dungeon would be doors that open only at certain phases of the moon. This would work best with large dungeons, or if you otherwise had a reason to return to it over time. Then the dungeon would cycle through different areas being open; the players might even need to complete some task or puzzle in one area to get further into another.
Some doors might be open for relatively long periods in the moon's cycle, others for only a single day. And if there was more than one moon, a door might open at certain specific combinations of phases. There'd probably have to be some kind of notation system, a code for the PCs to figure out, that indicated when these doors would be open, so the players wouldn't have to go through and check every door every time they entered the dungeon.
Other time-based doors are fairly simple to imagine. Doors based on time of day, days of the week, months, seasons, and specific times of the year would all be fairly straightforward, though, again, it's a good place for a puzzle, especially if the time when it opens is fairly specific, or a long way away. It wouldn't necessarily have to be code-based (my group likes codes); the information they need might be written down somewhere, or known by other inhabitants of the dungeon.
More exotic time-based requirements are possible. Eberron's planar conjunctions would make an interesting criteria; any fantastical, regularly occurring even would work well, especially if it was somehow important to whoever built the dungeon. (If it was built by mortal hands, that is.) Doors like these would also make a good place to use fantastic calendars. Using the contemporary calendar of the world would encourage the players to actually pay attention to it, while a calendar constructed specifically for the lost civilization responsible for the dungeon could help illuminate its culture and strangeness.