HK Disneyland is very accessible from downtown via MTR. Try to buy the entry tickets online via authorised travel company and you can enjoy some discounts. You can also skip the long ticketing queue. Disney experience will require a full day. As i have made my visit twice to HK Disney on different occasions, my advice is try to come during the cool winter season. Under 34deg weather, you will easily go  punctured  by afternoon. Do arrive at the time of opening if you want to maximise your coverage of rides and shows. Some form of strategy is required. Bring your water bottle and keep yourself hydrated. Water points are available at every washroom area. Food and beverages are rather pricey.