@ OP and everyone else, from our experience in ulduar 10 so far (which were only doing to get the proto drake )
the enrage timer has been set (dunno when) to 15 min.
when we did iron dwarfs, medium rare, 1 of our tank said "she's gonna enrage next time she lands so i'm going just going to eat, brb"
in the middle of the fight.
When he came back, around 4-5 min later we were still killing dwarfs
and 10 man hardmode timer has been set to 10 min, from our experience.