The resort monorail runs until at least 11pm each night. If the MK is open late it runs later....an extra hour and a half or two after closing. Sorry I forget which it is.
But it is a short walk to the TTC from the Polynesian. However, in the dark it can be a bit of a challenge. Watch for signs in the ground directing you toward it. From the beach, it actually a little confusing as the sidewalk doesn't continue in front of Tahiti.
I would suggest either watching from the dock area and then heading back to the GCH and hopping the monorail or walking from the GCH to the TTC.
Are you heading to the TTC to collect your car? There are no resort buses there these days (other than for SOG).