Hi Kate! Welcome to planDisney! Thanks so much for stopping by to ask this great question.
You're close to starting your vacation at The Happiest Place on Earth, and I'm so excited for you! You are correct that there is a
Disneyland After Dark: 90s Nite event on the date of your visit.
Disneyland Park will close at 8:00 p.m. that evening to all guests who do not have a ticket for this special event. Because your
Theme Park Ticket includes the park hopper option, you can enjoy
Disney California Adventure Park until 10:00 p.m. that evening.
At the time of writing this answer, you can still purchase tickets for Disneyland After Dark: 90s Nite if you want to enjoy more time at Disneyland Park. The fun that's planned for this event is totally rad, and the party lasts until 1:00 a.m.! If you decide not to purchase tickets to the event, there will be lots of fun waiting for you at California Adventure. I highly recommend ending the evening with the second showing of
World of Color - One, which begins at 10:15 just after the park closes.
If you have more questions, please stop by planDisney again. We're all ears, and we would love to help!
Wishing you magic,
Lisa