I was also wondering about City Walk. According to Universal's website, the students get exclusive access to City Walk from 5pm - 8pm. Not sure if this means all of City Walk or just a portion of it. I have copied and pasted below what I found on Universal's website.
CityWalk™ Pre-Party | 5:00 PM – 8:00 PM
Get your celebration started off right with exclusive access to the Grad Bash Pre-Party at Universal CityWalk™. Admission includes an unlimited buffet dinner, live street entertainment and DJs spinning your favorite music.