Does it matter what day to be in what park? The answer is definitely YES!!
When I talk to people about Disney I kid that if it’s Monday it must be Epcot. There is a reason for this. Historically, that is one of the best days for Epcot. With that being said it is usually one of the worst days to be at Magic Kingdom!!
Looking at crowd calendars is a great way to know which are best for you. There are many resources on this which include:
http://wdwprepschool.com/disney-world-crowd-calendar-for-the-2017-2018-school-year/ Also make sure to check the monthly day by day as well.
These are just a couple of the ones available (you can also find crowd calendars for Universal Studios). This goes under the category of “know BEFORE you go”, as it helps you while you are there.
Some of the factors that go into these are:
-EMH (Extra Magic Hours)
-New Ride/Attraction openings
-Weekends (locals or those looking to make a long weekend)
Hours for the parks are usually posted by Disney just over 6 months in advance, just in time to know which park to be in prior to make those 180 day dining reservations (hint, hint). Note: Hours and entertainment is subject to change. Also, note that refurbishment schedules are not always put out that far in advance. This means you may find out later that your favorite will not be open. I recommend watching the refurbishment schedule as well.
I hope this helps you with your planning and trip to Disney. This will be helpful for planning your days IN the parks.