They’re really awesome. I got on 21 rides in 3 hours for Studios 2 weeks ago, so a ride every 8.5 minutes including ride, travel, and ice cream time.
It’s only walk on for the party itself only. The park shuts at 9, and cycles out the non party people. Party starts at 9:30 and ends at 12:30. There may be slight lines early on, but people spread out quickly. People tend to gravitate to the big ride first (FoP and Slinky) then spread to the others, so I’d suggest starting with others and ending with Toy Story to maximize time. Star Tours was walk on for an hour before the party started.