I can confirm this as a Core level organizer - Advance level organizers can sanction up to 2 sessions while Core level organizers can sanction 1 session. Source: Alara Reborn Prerelease Solicitation document, WotC.
Alara Reborn Prerelease Tournaments can be run on Saturday, April 25th or Sunday, April 26th.
• Core Organizers may run one Prerelease on one of these dates.
• Advanced Organizers may run a Prerelease Tournament on one or both days. They cannot run two Prerelease Tournaments on the same day.