Frank Ocean was over an hour late (roughly an hour and ten minutes) taking the stage, therefore his set time was extended to 12:20am (20 minutes past the Sunday midnight curfew).
Frank Ocean was originally supposed to have a group of ice skaters (including hockey players from around the So Cal area) be part of his cast/performance, hence an "ice rink" was built in the middle of the crowd at the main/Coachella stage (with supposedly underground tunnels leading to secret entrances/exits) for this portion of the show, but Frank cancelled/nixed the idea right before going on stage.
Frank Ocean's performance was supposed to be on the webcast, but he cancelled that idea right before taking the stage.