pathfinder 1e – What type of action is the opposed charisma check in Charm Monster?

Scenario

Standard action, the bard casts Charm Monster.
The monster changes posture, it seems to have worked!

“Back up, I charmed it” – he yells to his allies (free action)

while gesturing at the monster to stop fighting (move action or fluff alluding to action for next round?)

Question

What’s the earliest he can make the Opposed Charisma Check to convince (Int 1) monster to back off and stop attacking allies, assuming all his allies immediately went full defense and that there’s no one except for the party and the monster there?