Hello, Carrie! Glad to hear that you will be making your way to sunny California next month.
It sounds like you will only have enough free time to visit
Disneyland Resort for just one day, starting in the afternoon. But it also sounds like that day is when
Disneyland After Dark: Grad Nite Reunion will take place. The ultimate decision will be up to you, but I recommend purchasing a
one-day Park Hopper ticket, and here is why.
If your ultimate goal is to see as much of Disneyland Resort as possible in less than a day, the Disneyland After Dark: Grad Nite Reunion event will only grant you access to
Disney California Adventure starting at 5PM. You will not have the option to explore Disneyland Park as part of the Disneyland After Dark ticket.
However, with a one-day Park Hopper ticket, you will have access to both parks. Additionally, you will have the option to visit
Disney California Adventure Park until 8PM and
Disneyland Park until midnight on June 28.
My last bit of advice is to consider purchasing
Genie+ with your Park Hopper ticket. Using Genie+, you can book
Lightning Lanes, which will grant you shorter wait times for select attractions.
I know you will only be at the Disneyland Resort for less than a day, but a lot of magic can be experienced in that time. I hope you have an incredible time, and please drop another question our way if there is anything else we can help with.
Happy planning,
Lola