I will be staying at Grand Mercure Shanghai Zhongya hotel. I want to an hour river cruise.

Walk from your hotel to the South Square of the South Train Station bus stop to take bus no. 930 to get off at Xiaodongmen. Then you can easily walk to Shiliupu Port at No. 501, East Zhongshan 2nd Road to buy a ticket and take the cruise. Or you can take a taxi to arrive there directly for a cruise. A regular sightseeing cruise takes around 90min.