If I book 2 nights and check out "early" at 8pm, will I still definitely get 2 qualifying nights?
My expectation is that you should get credit for the 2 nights, as you are checking out after the formal last-possible check-out time, which I believe is 6pm. I had a somewhat similar experience checking out at around 11pm and I got my EQN without any complications.
However the qualification "definitely" is something you can only get from IHG ...