Which bus goes from Hangzhou to Lishui. How much time it takes? What is the frequency?

You post the question here. Probably you wanna leave from the airport. If so, direct long-distance buses to Lishui are available outside the terminal building. They are scheduled at 10:40, 12:50, 15:10, 17:00, and 20:00. It takes about 3.5h to arrive and the cost is CNY120 per person.

If leaving from downtown, go to the South Bus Station to catch a bus and they leave at 08:40, 11:30, 13:15 and 16:05. The fare is CNY100/person.