I think you should go to the park first, since the market might not be fully opened in early morning. 1-2 hours is enough for the park and around 2 hours or less for the market would be enough.

I think you'd better go there after departure, since if you are leaving from HKIA, you don't need to take train back to Disneyland to pick up your luggages, you can bring your luggages to Citygate Outlets, store them there and visit big buddha, half day would be enough.

The check in time is 1500 hrs and check out time is 1100 hrs. Mostly they don't allow extended check out.