What is the visa processing time???

Dear Sir/Madam,

My daughter has received an Invitation letter from Harbin Institute of technology in China, to visit as a "visiting researcher" to pursue collaborative research and the research will be supported by The Hong Kong Polytechnic University-HIT collaborative projects.

What is the visa processing time for a case like this? She will have to visit Hong Kong Polytechnic University to start her work as a researcher as soon as possible.

Thanking you in advance,

SA