The daily hours are definitely less in summer now, as the MK used to be open til midnight every night in summer up until the early 2000s. BUT, I will say it has also sort of evened out if you look at the entire calendar because the park also used to close at 6 or 7p all the time during the week in Sep, Oct, Nov and Jan and Feb. So some hours are shorter now, but then some hours are actually longer than what they used to be.
The one thing they have definitely cut back on is how late the evening EMHs for the past 5 years or so and at which parks they are at.
Regarding hours changing, like eliza61nyc said, Disney could very well update them as it gets closer to your arrival date DisneyGirl3820. I've had instances in the past where Disney updated park hours a couple of times leading up to my trip, sometimes as close as only a week or 2 before! So it is very possible. However, with that being said, crowds have been much lower than expected this year. So if that trend continues into early fall, Disney may not be as keen on extending the park hours as much as they were in the last few years.