IME, the best moment to set up the trap is, when you CALL someone's raise and flop the boss hand.

Like:
22 + A2x r flop - check to the raiser, let him bet out his Ace, CR turn and of course call push. Or if he call CR, then lead out the river - value bet it.

Trips from pocket pairs are best payoffs, when raiser makes his hand on the flop too. If he doesn't make his hand or is a weak passive pussy, it's better to just bet your hand out.