If they are just a few months away from building a nuke if they choose to, then an attack can not stop them. Their will is the only thing standing between them and nukes, so there is no sense in forcing them to build nukes as a result of an attack. That means Bibi needs another enemy to focus on.
Rohani: Nuclear deal achieves Iran's goals (AP)
from the article: Iran will be able to build nuclear bomb within months, IAEA says