You can take a coach bus at Hangzhou East Bus Station to go to Haiyan. It takes you about one hour to get to your destination. The East Bus Station is located at No. 215, Genshan East Road, Hangzhou City.

Thank you so much for your advice.
By any chance do you know the coach timetable.
Do the tickets have to be purchased in advance?

I'm not sure whether the schedule that I know is the latest one. So, just give it to you for your reference.
There are 30 buses within a day from Hangzhou East Bus Station to Haiyan. The buses leave every 20 to 40 minutes from 06:40 to 18:20.
As I know, the ticket can be returned to the bus station 24 hours in advance of the departure. So, I guess probably tickets are sold at least one day in advance. You may purchase it at least one day in advance.
Ps: In Hangzhou City, you can take the following public bus to get to the East Bus Station:
B1, 19/K19, 20/K20, 31/K31, 33/K33, 35/K35, K47, K55, K201, K202, K205, etc

Hi again Evelyn,
Thanks again do much for your very useful reply. Can I bother you again for one more question? By any chance do you know of a good english-speaking driver/guide who can show us around Hangzhou for one day. 23rd July

Ms. Hannah, you are welcome. I am so sorry I don't know much about the English-speaking driver or guide in Hangzhou. I think you can post in the Community of TravelChinaGuide.com. I often see some overseas tourists give such kind of posts there and they could get much help through that.