Fast Swallow Ability

[Some Duck]

I'm running a creature with ability against some PCs soon, but I don't know when it is supposed to activate:

Fast Swallow (Ex):
The creature can use its swallow whole ability as a free action at any time during its turn, not just at the start of its turn.

If it grapples a person, does it get to swallow right then, or does it have to wait until its next turn to swallow (still as a free action)?

[Sandslice]

The creature can swallow as soon as the grapple is confirmed, same turn. That is what the ability allows.

[VoodistMonk]

I love Jotund Trolls...