Trip to Hong Kong and Vietnam

Good afternoon,
I have a Vietnamese nationality and a Dutch residence permit for 5 years. I am now living in the Netherlands. Over 3 weeks I am going to Hong Kong for 2 days before flying to Vietnam for a stay of 1 month.
Could you please tell me if I need a visa for a stay of 2 days in Hong Kong? If so, how long does it take for application?
Should I have my application done by a travel agency or apply by myself? As I have heard different opinions from the consulates about this, some say it takes only 4 days, some say it takes more than 1 month as they have to send the documents to Hong Kong for permission.
Thank you very much in advance.