Squeeze anything else? On a bad traffic day, you will be lucky to get there by 10pm, not even talking about eating a duck!
I don't know which terminal you are going to arrive in Beijing, the new one may take you quite a while to walk out. The new subway is your only option to get there, and I won't take a chance for taxi coming back to the airport. One block on 2nd or 3rd ring road, you will miss your flight. Strongly advice you to get back by subway.
Why you want to have a dinner in Hyatt? There are a number of good places for duck and closer to the airport. Even you got there before 8pm, will you enjoy it when you need to check your watch 6 times per hour?