The rate changes every day. You can search for the accurate rate through the tool of China Money Exchange(https://www.travelchinaguide.com/tour/currency-converter.htm) on this website.
It seems that the rate in the airport and Disneyland are higher than other places. In fact, you can easily find a money exchange angency/outlet in most places of Hong Kong and the rate may be different among those outlets. You'd better find a suitable one for you according to the rate. Addition, better exchange some loose change.

Thanks Ms. Katrina! I'm a bit anxious as our bus will take us directly to Disney Hollywood Hotel from HKIA and we're not sure where to find a good money changer.