Take the bus to MK. Walk to the Contemporary. There is a path on the right hand side by where the bus drops you off. It will take you about 10 minutes to walk. If walking is an issue then you can take the monorail.
I would leave the hotel room an hour before just to have time to walk to the bus stop, wait for the bus, ride on the bus, walk to the Contemporary. I doubt you'll need the hour but you are better off being early.