The Ark, isnt that what level 6 is? well if it is it depends on difficulty, on legendary if you keep trying it will take maybe 1-2 hours depending on how good you are..on easy maybe 20-30 mins..normal would probably be the same as easy, heroic would be maybe 30-an hour because on heroic when you need a landing spot for Foward Unto Dawn there will be a wraith and some stuff guys hiding in the rocks and 2 AA wraiths, thats the only hard part then you make your way back after you kill everyone at the landing zone (dont forget the tank makes things go easier, so get it) you will encounter 2 ghosts near the skull (near the landing zone) then you will face 2-3 wraiths (usally 2) when trying to get around the cliff then into the room where you need to abandon your vehicles and your allies take there vehicles in..activate the light bridge (and the terminal behind it) then walk outside and theres the scarab fight..get on the gauss turret and destroy the ghosts then quickly hop out (because its turned into a war out there!) and grab a tank..destroy the wraiths untill the scarab comes. go up the ramp to the right into the building where you will enocunter little resisitence going up (mostly jackals and brutes) go into the building ( and look at the dead bodies/ your guy getting zapped xD) then quietly meele the sleeping grunts and brute. you wont encounter much after tht (cutscene after you take out the room looking at Niagra Falls =p then heading back to kill more brutes) so yeah it depends on difficulty / how fast you can do it i guess around 30-1 1/2 hours.
