Hi Dana,
I wish there was a way to create your own itinerary on the Walt Disney World site; however, at this time there isn't anything quite like that. You can create your own,
custom maps that highlight family favorite attraction, and you can create your own
planning video with information customized to your travel needs. The video is helpful for planning, and the maps are a GREAT keepsake; however, neither of them will give you the hour by hour guide that I think you are looking to create.
There are other "unofficial" sites that do provide spreadsheet tools specifically for planning Disney vacations and maximizing your time. I suggest doing a search for, "designing your own Walt Disney World Itinerary." You will get listings for some helpful sites.
Hope this helps. Have a magical vacation!