From the time the dungeon is completed you have 5 minutes to exit the instance.

The timer replaces the duty timer as well. But 5 minutes is more than enough time to go back and grab treasure chests, take screenshots, read lore interactables, or grab a few missed mobs.

I love to grab extra loot when everyone else has left. No Competition and free loot. (I think I got some rare drops that way too.)