Hey there, Blaire!
Thanks for visiting with us!
If possible, I would consider rearranging your plans so that you can visit one of the theme parks that has longer park hours that day. Without a park hopper pass, admission into any of the other theme parks will not be granted.
On that day, the other parks are open until 8pm or 9pm, which will give you more time to enjoy one of those parks.
If you decide to visit the Magic Kingdom that day, you can upgrade your theme park ticket at
Guest Relations at any theme park and
Disney Springs or at the front desk of your resort if you'd like to continue enjoying the parks for the remainder of that day.
Enjoy your time at Walt Disney World!
Wishing you magic and memories!
Korliss