Ngaire, that is scary. Too bad you can't have it done while in South Africa. It looks like their express service is "next day" but it doesn't say anything about Americans being able to get their visas in South Africa (while Chinese Embassy here specifically mentioned Americans). Here is the link to Chinese Embassy in Johannesburg.

Chinese Embassy Consular Services

I was sweating ours and we end up having ample time. We went down to embassy this morning and passports will be ready next Monday. Our only "issue" was that we don't have alien registration cards so we had to make pictures of our id cards and go back to end of line.

BTW, they had bottles of glue at embassy for gluing on pictures.