Often they stay the same, sometimes they change.
You don't need to plan more than 6months out, and once the schedule is out, EMH doens't TEND to change. PARK hours DO change though as WDW gets more accurate data.
That said, though they don't tend to go away once posted, there have been times when WDW staff ADDED more EMH hours during one of our visits. If your vacation coincides with a holiday like Easter week, that's when you may well have MK go from one AM EMH to having EMH every day. (you might be ableto google park hours fomr past years, but beware of holidays that change year to year- like Easter. Crowd prediction sites do a horrrible job of factoring those. they also do a terrible job of accounting for variations in weather- which has a HUGE impact on crowds>)
I expect that AK hours and EMH might go up, as AK has the newest shiny objects (exciting additions), while perhaps slightly fewer folks will be totally gaga to see the Frozen attraction than they were last summer.
In the meantime.....if you really want to do some pre-planning.....decide how many days you want to go to each park, likely must-do attractions (or perhaps more importantly, the ones you feel you can skip), and which dining options most appeal to your group.
If you want to makeit easier on yourself- choose dining at your WDW hotel. Truly, that's probably going to be your best options anyhow. WE typically eat a Quick breakfast at our hotel every morning. for lunch, we either get ice cream, or just stop in whichever qS we happen to be closest to when it happens to be a convenient time to eat (if we go bakc to our hotel mid-day, it may well be at our hotel).
That just leaves dinnner. Other folks like to make lunch ADR's (instead of dinner). Some folks plan more ADR's, but I find that just bogs us down too much, especially because many WDW TS locations are buffets. Do yourself a favor, only book ONE buffet a day so you avoid feeling sick!
In all seriousness, if we have a buffet dinner, we often just skip lunch. We maybe share a few Mickey bars or some fresh fruit to tide us over. The fruit stands are your friend: cheap, quick, refreshing, no sluggish feeling.
I don't plan our rides much beyond our FP. Focus on the e-rides early if you can manage it. Otherwise if you see a long line, keep walking and return later. Unless it is like Easter week. thenh everything will be fairly busy. Your best bet on Easter week is to allow more time for anyhings that doesn't have a long wait, Luckily, that is ALSO often a great time to visit the gardens and hotel lobbies.
Seriosuly, again, weather is a huge factor. Not just your given day ether. If your first Sunday happens to be the first non-rainy Sunday in a while, then the parks will be more crowded. If your day is rainy/cold/hot/humid/etc, crowds will be lower. They just will.