visa interview appoitment policy in china changed, at least in Shanghai
1. they require you to pay the visa fee first, when you call for the appt,
they will ask for the fee receipt number --- a very awkward policy, which
requires you to find someone to pay the money for you.
2. for h1b you need to provide the 797 form number for the appt.
that was my own experience, and i did get the appt done yet since i did not
have anyone who can help pay the money for me. btw, you need send a copy of
your passport to your friend in order to pay the money.
so, it's not a good idea to go back before your h1b extension is approved.