You are correct to listen to the tour guide. Get the app in quickly after the app launches. Auburn does not require any essays, whether he does the Auburn self app or the common app. He can fill out some of the common app questions now, and it will rollover Aug 1 with the new app. I would say max one hour to complete the app.
Has he sent his official test score to Auburn? If no, I would do that now.
ETA: here are the common app sections that will rollover when the new app goes live:
Also cross posted with tamagotchi!