I completed the mine quest I got from Mantis and it updated my Journal saying I should go see him. Yet when I go to him, he doesn't do anything, all I get is a scene of him standing there. Do I have to wait for the duration he gave me to run out? If so, where do I see how many turns I have left?

Don't worry. You don't need to see him. The quest is done

I went and saw him after I completed it, he said something like : Not so fast young one, let us see what the others have to say.

i completed the mine quest (sister told me to see Mantid) and i got in his chamber and can't do nothing ,but i received a quest from Warden to kill Pangolin,and i didn't get the quest to remove the hearth from 1st Sister(shouldn;t that be the first one quest from brothers)
Anyway xapati just go trough the void harvesting or wathever and Warden will give u this quest ...

Ok, thanks

with the brothers it's a matter of 'no news is good news' even after you kill the pangolin you get bugger all from warden. not even a thank you. ungrateful bastard. can't wait to try and kick his arse.