Here's what I would do...
Go to your closest bus stop at SSR. Take an Epcot bus or a MK bus, whichever comes first.
If the Epcot bus comes first: At Epcot, take the monorail to TTC. Then walk from TTC through the Poly to the Ceremonial House. Or take the Resort monorail one stop to Poly instead of walking.
If the MK bus comes first: At MK catch the boat to Poly; Grand Floridian is the boat's first stop; Poly is the second stop. Or take the Resort monorail three stops to Poly instead of taking the boat.
Yes, a cab would be faster, but catching a cab at SSR is a pain because resort is so spread out and you would normally catch a cab at the check-in area. With the money you save by not taking a cab, you can order some extra items at dinner.
After dinner, take the boat from Poly to MK (nonstop). If MK is open, pop in for a couple of hours. Then take a bus back to SSR.