That’s how long John Bolton says Israel has to launch a strike against Iran’s nuclear facilities:

Iran is to bring online its first nuclear power reactor, built with Russia’s help, on August 21, when a shipment of nuclear fuel will be loaded into the plant’s core.
At that point, John Bolton warned Monday, it will be too late for Israel to launch a military strike against the facility because any attack would spread radiation and affect Iranian civilians.
“Once that uranium, once those fuel rods are very close to the reactor, certainly once they’re in the reactor, attacking it means a release of radiation, no question about it,” Bolton told Fox Business Network.
“So if Israel is going to do anything against Bushehr it has to move in the next eight days.”
Absent an Israeli strike, Bolton said, “Iran will achieve something that no other opponent of Israel, no other enemy of the United States in the Middle East really has and that is a functioning nuclear reactor.”
But when asked whether he expected Israel to actually launch strikes against Iran within the next eight days, Bolton was skeptical.
“I don’t think so, I’m afraid that they’ve lost this opportunity,” he said.