I'm an American with a letter from UNAIDS for a 2 week trip, and I need to get the China visa in BKK.

I've seen the fees and number of photos and the forms on your helpful site. I've been told that the address for the visa service is not the same as for the embassy. Where exactly should I go? Different sites say that hours are morning or afternoon/ When are applications accepted? When are passports returned to applicants?
Thank you.