is there any bus from hangzhou to yangzhou after 17.00 hr?

I'm afraid not. As I know, buses to Yangzhou are scheduled at the North Bus Station and the last schedule is at 17:00.

If you have to travel after 17:00, I suggest you take a high speed train from local East Railway Station to Nanjing East first in 2 hours. Then head for Nanjing Station to take another high speed train to Yangzhou within an hour.

Thank you very much.