If I stand right inside the park or on the train platform and leave right at the end of the parade, will I make it to 4pm HDDR?
I have the same exact question, but based on my research, it’s probably a 50/50 proposition, depending on if one gets the boat right away. Ourlaughingplace.com has a transportation wizard. Plug in from MK to ft wilderness. Can be as little as about 18 minutes, or as much as 34. Add in walking time embark, debark…
My best guess is that either you miss the end of the parade, or get to hdd a little late. It also depends on where the parade starts. If it starts on main st, 50-50. If it starts in frontier land, not a chance.
Also keep in mind (another liner told me) that there’s some nice things to do for kids near hdd, so getting there early might be a really nice thing to do for the kids. Also gets one out of the worst of the midday MK crowds. 
Hope this was helpful. I haven’t actually done this yet, but will be doing it in sept.
Go well. 
I have not attempted it so I do not speak from experience but I would think not. If the parade starts at 3 pm it won’t get to the end of Main Street until 3:20 or later. I think that the parade itself is 16 min. Then what if you just missed the boat and have to wait for the next one? You need to arrive early to HDDR so that you can check in and have your picture taken. That’s just my opinion though. Perhaps someone else will have had a different experience. 
I’m thinking we shouldn’t try it. Thanks for the advice. This is the sort of over ambitious touring that I would totally try.
Thanks for asking this question. I was wondering the same thing!