It will take about 3 or 4 mins to walk from the buses to the monorail station. Now, if it were me, I would consider taking the boat to the GF. Once you get on the monorail it will take you about 20 or so mins to get to the GF.....takes 25 mins to make the complete loop.
If you see a small boat coming in, from the Polynesian, head to the dock and get in line. The boat will then go to the GF before heading to the Polynesian. And it's a very pleasant ride. But, if the boat is just pulling away from the dock, it could be about a 15 mins wait for the next one. You can pretty much tell...if you see a boat leaving the GF and heading to the Polynesian, the boat will get to MK in about 10 mins or so.
I usually take the boat over. It tends to be quicker and more relaxing.