And what are the consequences of NOT acting? When will the right time be?
Today I'd say the consequences are pretty much zero. And I don't think there is ever a right time for such actions, just the time you've got to take such actions.
Personally I'd work on securing the Iraq-Iran border, strengthen the Iraq defence forces, especially the Kurds, and install some nuclear weapons along the border by invitation of the Iraqi government. Then as I said make sure it is clear that there will no hesitation to use them to ensure the destruction of Iran if Iran ever attempts to use nuclear weapons.
(But of course the above is all too simplistic - but hey it's good to pretend you're a superpower sometimes and that human lives mean nothing.)