From what time to what time is the impressions of west lake shown?

The show time is at 19:45 at night and it lasts to 20:55. There is no direct bus then, so you may need take a taxi to reach local Railway Station in about 30 minutes to catch the last bullet train to reach Shanghai.
The last bullet trains is around 21:38 at night.
In my opinion, you will be in a hurry if you plan to catch it. If time is possible, it is suggested to stay one night in HZ and then take the first bullet train at around 06:14 to go to Shanghai.