Reading the lore in dungeons

[Meimi_chan]

The timer actually disappears when you beat the final boss. I'm not sure if it's still ticking in the background somewhere but I've yet to run out of time..

Actually there is a timer, I remember staying behind after successful Amdapor Keep runs to try my luck for the minion (never got it anyway like that... Did it unsynched and got it the first time), and after a bit I would see the notification "5 minutes remaining to complete the duty".

Edit: the runs were probably 15 minutes long, after the boss died I would return and go for the chest, I remember getting the message after I had to run all the dungeon again because I accidentally aggroed monsters along the way.