Beijing (Main) Train Station to Terminal 2, PEK: Metro 2 and Airport Express transit time

Hello,

in mid December I arrive from a remote rural area by train (hard-sleeper, only 2 trains per day).

My International flight back to Europe departs from Terminal_2 at 13:40h.
Now the BIG QUESTION: Will I be safely in time if I take the train which arrives at Main Station at 09:40h?
Is my assumption correct, that travelling by Subway (Metro_2 from the Train Station to Dongzhimen, and from there via Express Train to T2) will be more than twice as fast compared to the Shuttle Bus, independently of rush houyr traffic jams?

The only alternative to this option would be arriving one day earlier at 20:00h, hence my question.
The flights are already booked.

How long before departure will the boarding close at PEK?

Many thanks, and a pity I didn't know your website before 2015 for train bookings.

rgds.
Michael