Terminal 8 can be either of the extremes in the morning, nearly dead or looking like Times Square and there is no rhyme or reason of when. If you have OLCI and have no bags I would say a least an hour as Security lines can be long and even the Premium lane dumps into the masses. Full of travelers going South that speak little English and don't understand the rules (a few weeks back there was a woman crying like crazy because TSA would not let her carry through a bunch of large bottle liquids).

Also, if you want time to eat and/or go to the bathroom add more time. Finally, if you are traveling on a wide body the GAs usually start boarding about 40-45 minutes out even though the BP will say 30 minutes out. Of course, if you are in Groups 4-7 it will be another 10 to 15 minutes before you board anyway.