Just mind you , that you need to purchase 3-zone train ticket at 2,80€ to get from SXF to Berlin. It used to be 2 zones, but this has been changed recently.

Donīt expect any open ticket office at this hour, so have some coins or smaller notes ready for the vending machines.

You can see the schedules at:
http://www.bvg.de/index.php/en/Bvg/Start