It was posted on the General UC board that is is April 9. I can’t get into the website but if you google Bruin Day 2022, it pops up with:
UCLA Bruin Day 2022
An exciting day on campus for admitted students and their families Freshmen: April 9, 2022 | Transfers: May 14, 2022.
Edit to note that UCD, UCSB, UCR and UCLA will all have their open houses on the same day.