You can apply for a job six months after your graduation. If you have graduated from RHK and you start the process of obtaining your visa within six months after graduation, you will not be required to have an offer of employment as a condition of receiving your visa under the Immigration Arrangement for Non-Local Graduates (IANG).
Applying after six months have passed since graduation: If six months have passed since you graduated from a Hong Kong university and you are applying under the IANG, you must have secured a bona fide offer of employment when you apply.
Your visa and residence permit will be good for an initial period of one year. You may apply for an extension to your visa after this time for a period of two years. The second time you extend your stay, your visa will be valid for an additional two years and the third time you extend your visa it will be valid for a period of three years.