Transportation from Beijing to Badaling

Have I interpret your schedules correctly for Bus 877:

06:00-12:00(Apr.1-Oct.31) are departure times to Badaling

10:30-17:00(Apr.1-Oct.31) are departure times to Beijing

How frequent does the Bus 877 come to Parking lot north of the Deshengmen Arrow Tower and then again from Front Hill of Badaling? You indicated this bus is non-stop between Beijing and Badaling; where does the other two buses stop that it takes 30 minutes longer for the trip?