Er, about 1-2 days for Shanghai, 1 day for Suzhou and 2 days for Hangzhou, plus the transfer time, i think you need about 5-6 days.

All depends on what you would like to see in these three cities. Once, I have spent 4 days in Hangzhou but still felt not enough to view this charming city. Last year, I have used three days to travel in Shanghai and Suzhou. That is really a rush tour by myself. Alternatively, if you would love to pass all of them effectively, you should consider participate in a tour group which could save lots of time.