I am flying into shanghai on 23rd august and boarding a cruise ship on 26th August.

You are eligible in principle, but you should have in mind two "little" conditions:

- You have to fly to Shanghai on a flight that does not have any additional landing in mainland China beside Shanghai and it should not have a landing in the country where you will be going after your departure by cruise from Shanghai.
- Your cruise should not have a mainland China port call immediately after you leave Shanghai.

To conclude, if your itinerary looks like: Sydney - Shanghai - Busan (South Korea) this is fine.