We plan on leaving MK on July 2nd for lunch at Kona and doing 1/2 day Epcot and 1/2 day MK on the July 3rd. I am concerned about crowds during the holiday. Is there a chance that we could leave for lunch or to switch parks and be denied entrance due to crowds? What is the best time to leave the parks to return to resort to avoid the massive crowds? How long should those breaks be? We are doing dinner package for Fantasmic show at 9. After Fantasmic where should we go to view fireworks at HS and what time are the FW? Any suggestions for us since this is busy time of year appreciated. We are with college age kids. Thanks!
The 4th of July is one of the most crowded days of the year; TP lists MK as a "10" - and it will likely be a "crowded" 10. TP lists the 3rd as "only" an 8, but as this year the 3rd falls on a Friday AND is the Federal Holiday; I think that "8" is going to be closer to a "10" (TP does not do a great job in accounting for these kinds of variables).
Where you are staying can have a lot to do with park closures. I don't remember all the specifics of the the different phases of closing (I never go at crazy-busy times, so I don't pay that close attention), but if you are staying on site and/or have an ADR you are less likely to have a problem getting back in. I'm sure others can provide more detailed info and/or the link to the page that discusses phase closings.
EP is huge; I've never heard of phase closures there so you should be fine (although it will still be very crowded).
If you mean leaving the parks at the end of the day, to avoid crowds you want to leave either before the night-time show or about 45 min after the show. MK and EP are horrible for this after Wishes and IllumiNations, respectively. The crowd leaving F! at DHS can be daunting, but otherwise that park is not too bad. No issue at AK as there is no PM show. If you are talking about mid-day breaks I don't really think there is a "best" or "worst" time; just kind of how it fits into touring plan and how long a break that you want. Personally, I don't take mid-day breaks - but then again, I never go during the heat of the summer.
I believe that the FW at DHS will be at 9:45. As F! ends at 9:30, and there will be a crowd leaving (I recommend sitting near the back), head towards the center of the park and get as close as you can before they start. The only time I did both on one night I watched the FW first and went to the second F! show, so I don't have first-hand experience on doing it the other way around - but I'm sure that there are others who have.
If the "college kids" are 21 or older(and for you and DH), don't underestimate the benefits of occasional "beer stops"; it can really help with dealing with the crowds in EP and especially DHS