You can take the shuttle bus from Tangkou to Taiping at Tangkou, and you can go to Emerald Valley. There are many buses on this road. You just need to wait for the bus on the road. Tell the master that you are under the Emerald Valley, and they will stop you. Then you can wait for the bus from Taiping to Tangkou on the way back. The latest departure time there is 17: 00, so it's almost 17: 30.
If you take a bus to Hangzhou in the afternoon, there are three trains, 14: 30, 15: 30, 16: 30, which can be reserved. You can ask your hotel to make a reservation for you, so you can wait for the bus at their hotel, and they will also help you contact, saving you a lot of time. If you don't ask your hotel to make a reservation for you,