Hi, Lydia!  Thanks for bringing your question to planDisney!
You've chosen a spooktacular time to visit The Happiest Place on Earth because it's 
Halloween Time at Disneyland Resort!  Be sure to 
pose for a photo in front of the adorable Mickey pumpkin on 
Main Street, U.S.A.  While you're strolling through the park, you just might bump into some of your favorite 
Disney pals all dressed up in their Halloween best.  Be sure to experience 
Haunted Mansion Holiday, and end your evening with a performance of 
Halloween Screams.  You're certain to have a frightfully fun time!
I took a look at the 
hours and events calendar, and the 
Disneyland Park hours for October 21, 2023 are currently listed as 8:00 a.m. to 12:00 a.m.  Please keep in mind that hours and events are always subject to change, so I recommend consulting the schedule again closer to your visit for the most up-to-date information on park hours and showtimes.  If you haven't done so already, I would also recommend downloading the 
Disneyland mobile app to have all of this information at your fingertips when you're on the go in the parks.  
Lydia, I hope you have a ghoulishly good time visiting 
Disneyland Resort during the spooky season!  See ya real soon!
Samantha