How long one can stay in PRC on a S1 visa?who determines the length of time I can stay?

Usually, the S1 type is issued to those who want to stay in PRC for over 180 days. So it’s possible for you to stay for more than 180 days by S1 type.
How long you can stay mainly depends on your situation and the final decision is made by the consular officers according to the documents you provide.