If I were planning a long midday break on a day on which I was visiting MK and starting at rope drop, I would save my 3 FPs for the evening and do as many things as possible without FPs before lunch. By "blowing through" those valuable 3 FPs that you can reserve ahead of time, you may find that you are using them on attractions that don't have long standby lines in the morning.
For example, for someone who is interested in these things, you could get FPs for 7DMT, Anna and Elsa, and Space Mountain with return times of something like 5-6, 6-7, and 7-8. At rope drop, you could go directly to Peter Pan while the masses are going to 7DMT and A&E. Then you could go to BTMRR, Splash, JC, POC (if it's open), and HM. In those first two hours, and taken in that order, those attractions should all have short to manageable waits. Then, before lunch and your break you could do another thing or two, such as some of the "anytime" attractions or anything else with a reasonable wait. Then, when you return in the evening, you will have your 3 big FPs and can still see the parade and/or fireworks. After you use your 3 FPs, if you plan to stay later, you could so some more attractions as lines get shorter and possibly get another FP or two. That approach gets you two blocks of time in which you are doing attractions.
Another possibility would be to use one FP at around 11-12 and save 2 for the early evening with the possibility of getting a 4th (and more) after you use the 3rd. Of course, availability and selection for the 4th FPs will depend heavily on the crowd.