As others have said, the check-in opens 3 hours prior to departure, no earlier.
You should get access to the Air China First Class Lounge above gate 71. I found it to be pretty spacious with comfortable chairs and a nice buffet selection (mix of Chinese and western) and an ok drink selection. There was enough seating, which is always important IMO. I think the lounge works well practically and makes for a decent pre-flight meal. If you you have rich tastes and want an ultra-luxury and exclusive atmosphere, this is probably not the lounge.