There are other places that promote viewing manatees but as Steve/Jets70 said, October or early November is still not quite the season yet. Manatees gather in certain Florida waters that are at a constant warmer temperature than the ambient ocean temp. Thus the colder the air (and then the water) gets, the more likely you are to see manatees.
Florida has a number of fresh water springs that spew thousands of gallons daily which are at a constant temp year round. If you are coming down I75/Turnpike to WDW, there is an area due west of Wildwood south of Ocala called Homosassa Springs and Crystal Springs that has some "See the Manatees", "Swim with the Manatees" (never EVER touch one) places, and there are private campgrounds and rv parks nearby. You could try those on the drive down to WDW or on the way home (use google to find them and possibly call to determine if the manatees are there yet). If you try a day trip from the Fort, it's gonna be a longer drive each way.
Just up I4 through Orlando on the way to Daytona in the town of Orange City is a Florida state park called "Blue Spring SP" which is adjacent to the St. Johns River which is a popular manatee viewing area in the viewing season. The River empties into the Atlantic at Jacksonville but the origin of the river is in Central Florida and there is a large freshwater spring on a short tributary of the river next to the State Park (a short walking path connects the campground to the river boats where there are cruises/tours and a walking boardwalk to the spring). I am staying there between Christmas and New Years. It caters to a lot of day trippers in the season but for you to do so means a run up through the construction zone in Orlando.
Honestly there are possibilities and opportunities available from WDW but it might simply be still too early/warm but do the research and contact the place of your choosing to see what the situation is then.
Good luck!
Bama Ed