When do team rocket open the cave on island one in fire red?

Team Rocket doesn't open any caves on Island One in FireRed. They only appear at the Power Plant on Island One.

Here's a breakdown of the events on Island One in FireRed:

* Island One: You first encounter Team Rocket at the Power Plant, where they are trying to steal the Silph Scope. After defeating them, you receive the item and can then access the Silph Co. Building on Island Two.

There are no caves on Island One that Team Rocket is involved with.