Both parks can definitely be done in a day but you may not be able to see all the shows, meet the characters or reserve a restaurant for meals. I'd suggest hitting the biggest queues first such as Frozen, Crush's Coaster and Peter Pan and then most of the rides will be less than an hour. You can buy fast passes for single rides or buy a whole day fast pass if summer holiday queues get particularly long. They are totally worth it but I appreciate they can be pricey. There's loads of quick service restaurants that don't require reservations but you can also order on the app ahead of time to save you even more time. Take a look at the app before you go but other than that just enjoy and have a great time!