It's a wise idea to do a bit of preplanning in order to help ensure you make the most of your vacation and stay within your allocated budget. After all, unless you'll be staying in Orlando for a long period of time, it's impossible to see and do everything. Thus, you need to make decisions about how you'll spend your time.
As you plan your itinerary, make sure to obtain input from everyone you'll be traveling with. Also, leave plenty of flexibility in each day's schedule. Allow ample time to explore and enjoy experiences as they happen, without worrying too much about staying on a timetable and getting to the next preplanned activity.
In most cases, creating an itinerary with plans down to the hour or minute might make you more organized, but it will also create a tremendous level of stress during your vacation as you run around trying to stick to your schedule. Be sure to leave time in your schedule for travel between destinations, meals, and rest/relaxation.
For the purposes of preplanning your itinerary and visiting theme parks, it's best to divide your day into three chunks of time: morning, afternoon, and evening/nighttime. Keep in mind that you'll most likely be altering this itinerary once you arrive in Orlando and start actually experiencing your vacation.