I think the limit for transit passengers is 72 hours, so you may actually need to get a visitor visa. If so, you might need to start getting on with it.
We have just got our Visas by visiting the Visa office in London, which we did on a Monday and had them back in the post 5 days later. If you have any other questions about the process let me know.
There are plenty of spurious sites but this is the 72hr transit Visa page from the official site:
Policy regarding visa exemption for 72 hour transit in Beijing and Shanghai airports for certain countries