As I am reading and learning, I know that we will have to rely on Fastpass for those rides that offer it and we care for for the kids (arrival after opening). I am wondering how the planning through the seemingly helpful Touring Planning app can help as one never knows if Fastpass will be available, at what time and if availability would be at an acceptable time. I am kind of “stuck” on this. Does it help to spend time, regardless, with the application and optimizing it with the above in mind?
Yes, with a caveat. The app does a good job of optimizing and planning based on the ridiculous amounts of data from everyone. It predicts, based on the past, what time FP will be available if you get them at a certain time. Since it is just an average, there is always room for error, but the times are usually close to what they say.
An example: to get a FP at rope drop for Radiator Springs, the app will ALWAYS say it takes 20 minutes. I have never had this experience. I think this is a holdover from when they first came out. That means that if I go straight to get that FP, the time that was predicted is usually not the time that I get. This is where your flexibility is key; you have to be ready to go a little off plan as needed to make it all work. Take some time as you plan to decide what your priorities are–do you need to have every minute planned out? Is it more about the experience of being in the parks? Are there things that are “must dos” on your list, and the rest will just be as you go? Knowing before you get to the park how you will handle the changes that WILL happen to your plan makes the stress a lot less, in my opinion.
Long answer, sorry. Bottom line–the app is invaluable. Even better is using the app in park to adjust as you go. Have fun! 
Thanks for the wise words and clarification. I understand, we will be as flexible as needed. I am classifying attractions (based on what I know about our grandkids), so yes, there will be some that will be high priority. I will focus probably on the morning and maybe do what we didn’t get to in the morning, after an afternoon break while the parades and Fantastic happens. If something will be left out, hopefully there will be a next time. The important part is to have enough fun to justify the exorbitant price, probably our most expensive trip ever. It is supposed to be a fun, enjoyable experience not a major stress…
I am glad to know that while one cannot count on “precision” w. the plan, using it is not a waste of time.
One more clarification re. using the app, please. I would like to use the 2 day plan w. kids as a base and modify it to meet our list of attractions, breaks, etc. as needed. Is the Day 2 plan somehow linked to the Day 1 plan or are they independent? If I add an attraction to Day 1 which initially is part of Day 2 (in the off-the-shelf plan), would it be removed from the Day 2 plan? Thanks.
They are not connected and once you modify, one will not effect the other.
Thanks, now I know what to assume as I am making changes.