In Houston, documents can only be expedite it they are walked in. There isn't an expedite option for mailed in documents. Mailed documents can take 7-10 business days.
True, the information is hard to find. I remember reading you can walk it in, but I don't know where I saw it. I know it was somewhere. Maybe I saw it on a courier service?
It is #5.
http://houston.china-consulate.org/visa/english/yj.htm