Understanding Frightful Aura and Frightened tick down

I have a question concerning Pathfinder Second Edition:

From my understanding, when a creature enters the Lich’s Frightful Presence aura, it has to roll Will save.

Because of the nature of Frightened, every time the creature’s turn comes, it ticks down by one.

So within two turns, the aura is completely without any effect for the next 8 turns. (Gain immunity for 1 minute).

For an example of why this is weird to me: The party of adventurers made it down to the Lich’s evil lair. Beyond the door, the Lich Xarxark the Terrible awaits. The adventurers are Frightened by the Lich’s aura that permeates through the door. As the Rogue takes turns to unlock it, the Frightened value ticks back down to 0 and now the party is ready to face the Boss, undaunted.

Is my understanding correct?