The question reads:
I have tried everywhere to find if we can do a trip from Shanghai to Hangzhou, staying overnight and coming back to Shanghai via the Hangzhou Bay bridge. Is it possible if we took an early D train to Ningbo and then made our way over the bridge by bus or cab? Any suggestions you have would be more than welcome.
The short answer is, you don’t to go over the Hangzhou Bay Bridge from Shanghai to Hangzhou. Actually, there is no need to use that bridge from any where in the world to get to Hangzhou.
Shanghai, Hangzhou, and Ningbo form a big triangle around the Hangzhou Bay. Hangzhou and Ningbo are on the east, and Hangzhou is on the west. The Hangzhou Bay Bridge connects Shanghai and Ningbo, by passing Hangzhou.
So, if you want to go from Shanghai to Ningbo, the Bay Bridge is the best choice.