It normally takes 4 weeks to process a visa approved from HK Immigration Department. If you want to visit Macao, you are required to apply for it in advance through Chinese embassy or consulate in Dubai, and possibly you need to send applications to Macao Immigration directly. It also takes time for processing, so, you may need to arrange your schedule for visit. For Hongkong tours(https://www.travelchinaguide.com/package/hongkong/) , the invitation letter is not necessary if you will provide hotel bookings, round trip air tickets and better provide the travel itinerary from a travel agency.