I would check the time for the next Magic Kingdom bus(you can check on the App)and see how long the wait at OPR would be.TO MK and just Uber over to Cont to get there more efficiently and enjoy more of our limited time for the quick trip?
Personally I think unless it is showing a long wait,I would just go bus.
The bus takes you straight to the MK,while with Uber you would still have the walk to MK to do(Minnie Van will take you straight to MK but is expensive).