Can We can process Hong Kong Visa on urgent basis, Kindly advise procedure & time taken ..?

if you apply for visa to visit/transit HK for the first time, you should apply directly to the Immigration Department of the Hong Kong Special Administrative Region (HKSAR). There is no express service.

If you submit visa application to China embassy in Kathmandu, you can try to ask for the express service, it is up to the decision of visa officer.