Conversation so far:
how long is the bullet train ride from beijing to shanghai
The travel time by high speed train between Beijing to Shanghai is about 4.5-6 hours.
what's the length of the bullet train from beijing to shanghai
The high speed railway measures 1,318km (819 miles).
can I travel overnight on the bullet train from beijing to shanghai
You can travel between the two cities by the daytime G trains, taking 4.5 hours or the overnight sleeper.

Question: what's the travel duration
Self-contained rewrite: what's the travel duration of the overnight D train from beijing to shanghai