Number of Entries into China

I was advised to apply for a Single Entry visa for a cruise visiting 2 ports in PRC. After reading the many posts on this site I am conflicted as to the number of entries I require to enter these ports.

With the Single entry I have can I enter one of these ports twice on consecutive days for shore cruises. I will be in Shanghai port for 33 hours and 36 hours in Xingang.

Or, can I apply directly at the port for more entries.