I was way off the mark time-wise, wasn't I? Now that I know your arrival and hotel, that route you chose is the best one.
And just to clarify the hotel affiliations for everyone else:
DISNEY HOTELS: Ambassador and MiraCosta
OFFICIAL RESORT HOTELS: Those located in Maihama near the parks.
PARTNER HOTELS: Those located in Shin-Urayasu area.
GOOD NEIGHBOR HOTELS: Those located in Tokyo and other parts of Chiba.
Be careful to make sure which shuttle bus to take to and from the Parks. It might just be better to take the train from the Oriental, the station is in front of the hotel.