Is there a night bus from downtown to Beijing Capital Airport?

Hello.

I have a flight from PEK at 7.50.
Check in closed at 06.20.

The first express train to go to airport is at 6.00 and take 35mn.

It is too risky.

Any chance of bus leaving between 23.00 and 4.00 to go to the airport from downtown? Night line from downtown?

Thank