Typically, the buses seem to go in the resort-park-resort-park loop, so if the bus is running to MK, they'll be running back to the resorts. It might depend how early you want to be at YC - sometimes a ride share or cab is your best bet. You could also consider taking the bus from WL to Hollywood Studios, then make the 3/4 mile walk to YC - or grab a Friendship boat to YC marina.