I disagree. The best time to use it is when you need to use it.

Provoke is only useful when a target turns away from you. And when a target turns away from you, you'd better not be waiting for your RoH combo. Provoke and shield lob or whatever combo you have on your hands, even shield swipe will do.

Provoke is not a enmity building tool to be used in a rotation. It's an oh-no button.