I am thai who using tourist visa living in SH but I am applying for Z type

Hi there, I am thai and living in Shanghai , my current one is L type but now i have an invitation letter issued by the chinese government. I would iike to know ;

1. How long does it take for the Z type applying process in bangkok. I would like to pay extra fees to fasten the process because i have to get back to work in Shanghai.
2. regardless to the documents providing by the chinese government that i already have, what other documents or form do i need to prepare.
3. Is there any agent who can help me apply for this type, if yes please kindly recommend.

Thank you in advance and hope to hear back from you very soon. I need to book the tickets back to shanghai.
:D