We usually go from opening to about 2pm, but we have been many times so don't feel like we need to do everything. We haven't done the panda tour, but every program we have done there has been great, especially ones that go behind the scenes. Try to do the introductory bus tour regardless as it gives you a nice overview and saves you from feeling like you have to walk to all the areas. It lets you use the hop on hop off buses later too. Like Disney, rope drop is your friend!