what is quickest way to great wall from PEK. Then to forbidden city & back to PEK. Arrive 5A, Dep 5p

As for your case, I would recommend you hire a taxi upon getting to the airport. It would be best for a round trip: PEK to Great Wall (I presume you wanna visit Badaling Wall) and Great Wall to Forbidden City
The general cost would be CNY500 or around.

After your visiting at Forbidden City, you can count the time to decide whether to take a taxi or use public transportation. Anyway, here is the way by public transportation:
walk to Tiananmen East metro station to take subway line 1 to Jianguomen, where transfer to line 2 and get off at Dongzhimen. Nearby you can take the Airport Express to PEK.

Thank you so much for answering. Actually, I could not put the question properly for space constraint. The Q was mainly for managing time. I have certain assumptions.
1) Even on a weekend the Beijing traffic is very congested
2) Subways transport is not affected by traffic mayhem
3) Some segments of Wall is easier to access and closer from the airport.
which one? Badaling vs Mutianyu Great Wall

Now please correct me if I am wrong. Since airport is outside the city Airport Expressway should not be affected by Beijing traffic and we should be able to travel in 90 minutes. We actually wanted to rent a car for the whole day, go to Mutianyu Great Wall (2 hrs- by 8am), and ride the cable car and see the wall (2-3 hr, 11 am), take taxi back to Nunshaq subway line (noon). Take subway to Tianaman west (max 1 pm), see around for 90 min and leave for airport (230 pm) via subway-airport express and be at airport by 330pm.
Is this too tight and unreasonable?
Generally speaking how bad is BJ downtown traffic on a sunday morning in late november?
How long does it take maximum from Tiananmen East to Jianguomen to Dongzhimen?
Thank you again, really appreciate the responses.