PC Legion of Superheroes vs Galactus

This is the Silver Age Legion of Superheroes. They have three days of prep time before Galactus arrives to consume Earth.

Galactus is at average levels/moderately hungry.

How goes this?

Galactus gets stomped

How do you prep for Galactus with PIS off? You don't because it's impossible.

Galactus devours earth.

Galactus withdraws. He doesn't actively engage in fights to drive defenders off the world he wants to eat.