Do you mean you want to book the hotel for 3 days? I think you can do that, but for the visa question, I think you need read the requirements carefully.

hi.
I come to Shanghai in October.
Is there a market like The Silk Market in Beijing?

Hi,
you can make reservation in advance. In case you need to change, just call the hotel.
shanghai is a small city, but combined with west and east in many ways. The longer you stay, the more superise you will find about her. Given you have only 3 days in SH, you can experience the city in these respects: Food, Shopping, and Historic sites
The Yu Garden where you can find local traditional snacks and acient chinese building.
The south Bund Fabric market, where is a very popular place for customer made clothes. One piece of garment will take at least 7 days. So, if you stay longer here, you can make yourself a new suit.
The Bund, a wellknow landmark in Shanghai. World class brands establish their flagship stops here one by one - Cartier, Armani, D&G, Chanel etc. At night, the sightseeing is especially fabulas. you will love with the city.
Xin Tian Di is another landmark in Shanghai, popular in Foreigners circle. It's located at Xin Ye Lu, LU Wan District. you can take line2 to get there. Cafeshops and bars, Bistro, Resturant and a highclass shopping mall gather the place.
Huanghai Rd, Nanjing Xi Lu, HengShan lu are the other popular streets here. They were zoned to French concession, so the buiding/housing struture there still remained alot the old western style.

Hangzhou is "the garden of Shangahi" as we say here.
Only 38mins if you take high speed rail from shanghai to Huangzhou. city people usually go there for a short relaxing trip. But the fact is many people go there, how much relax you can feel?

Another city is suzhou where you will find slow pace and less modernized than shanghai or hangzhou but more green. Suzhou was full of private gardening of high-class officials in ancient China history. If you like to enjoy a slow and green trip, go there.