There's is a lot you can fit into your two hour blocks. A stroll along the Bund at night is a nice option or a little shopping spree on Nanjing Lu. There's a subway stop near the Grand Hyatt that connects you well to Puxi. I wouldn't take a taxi from Pudong to the other side of the Huangpu river, because the time you will spend in traffic jams can easily exceed your two hour limit.