Thought I'd make a note here since someone's tried to keep a recorded range on the wiki, but I just managed to score a 186 (3 min 6 sec) in Defense Up time from Iron Heart Attack orbs. Collectively of course, but I'd been influencing a lot of orbs that were buffing for like 119 seconds alone.
It WAS on Normal mode though, so maybe the difficulty level has an effect on it too, as I've never scored that high on elite.
Or maybe I just got reeeeeally lucky........several times in a row......
I was under the impression that each orb gave exactly 15 seconds. However, if you go down the elevator with the defence buff still active, the time you had left will stack onto the first orb you pick up next floor.