Recommendation for D&D players who want a faster dungeon/questing game after dinner?
For Dungeon Questing, your best bet is, sadly, long OOP¹: the GW game HeroQuest² or it's sequels Advanced HQ and Warhammer Quest. Note that the rules are available for free from Hasbro, but the bits aren't, so if you find it on ebay, you can replace the rules.

Another excellent, light, but not actually short, ans sadly in between printings, game: Wiz-War. (The more expansions, the longer it plays...)

If your players like medium length (30min to 2 hours) PVP, Dungeoneer (Example: Tomb of the Lich Lord is also excellent. It's a series of standalone games (which can be combined) of dungeon-crawling hack-n-slash. It is PVP, tho', and brutally so. It can be a blast with the right players, tho'. 

Order of the Stick is popular; if I could stand OOTS at all, I'd probably enjoy the game, but the art is utter drekh, and interfered with my ability to enjoy the game. It's also longer than I care for.

Another fun one, very different, is Aye, Dark Overlord. It's not of need a dungeon crawl, but the descriptions needed are usually dungeon crawl-ish.



¹ Out of Print
² Not to be confused with the Issaries RPG of same name.