If you have hoppers and staying on-sight it really easy.
After dinner get the Mono-rail to TTC then to MK . Show your Ticket and Resort key ( may be the same thing if on package) they will give you a wristband and have fun . It's really that simple.
You can arrive at any time before or during EMH even if it's just for the last hour as long as again you have admisson and staying on-sight