Too many variables to give you an accurate answer.
If the MK is still open, you can simply walk over to the bus stop and take a bus back--depending on the wait time 30-45 minutes total including the walk. Add 15 minutes if you take the monorail to the MK.
If the MK isn't open, you can take a bus to DTD and transfer from there to POR. Plan on 40-90 minutes, depending on how long the waits are for buses.
Or you could speing for a $15 cab ride and be there in ten minutes.
Anne