Just returned from the Tokyo-Hong Kong Cruise. You will need a single entry visa to enter China. The ZVS website became available 90 days
prior to the cruise.
We used ZVS and had our double entry visas within 10 days.
If you are doing a POST-cruise excursion back into China from Hong Kong,(i.e the Terra Cotta warrior excursion) you will need a double entry visa. One couple on our cruise erroneously assumed that their visas were covered by the ship. They were unable to go ashore in China on the cruise. China will not grant visas on short notice to tourists without visas, since the U.S. does not grant Chinese visas easily.