Tesla CEO Elon Musk has pushed the Hawthorne event back twice now. Originally, the party was unofficially set for September 28. However, it was tentatively re-scheduled for October 26. Finally, "Save the Date" invites were delivered for the new date. At that time, we thought it was set in stone, however, that wasn't the case.
The soirée was then moved to November 16th (and this was not specified as "tentative"). According to Musk, it was delayed due to Model 3 production bottlenecks and increased battery production to aid in the hurricane-related devastation in Puerto Rico. Now that official email invitations with accommodations and specific details have been delivered, the event will likely proceed as "re-planned".
Tesla has even gone so far as to say it will cover and travel/accommodation expenses incurred because of the schedule change. Teslarati was able to secure a copy of the official email.