First, to DisBoards!
You will probably hear two schools of thought. Arrive very early or go at park close.
I am a morning person so in early August I arrived at the park at 7:30am for a 9am opening and, after waiting at Security, the tapstiles, and the rope to Pandora, I “walked on” FoP from the rope drop. I was back out in front of FoP by 9:01am.
So I waited for a little less than 90 minutes. I would guess that for a dark (sunrise is ~7:20am), chilly (average low temp is ~47F) mid-January Morning Magic Hour you could probably arrive closer to 60 minutes prior to opening and still have a reasonable wait.
Wishing you a visit!