The tentative agreement to end the war in Iran and reopen the Strait of Hormuz would be good news for the global economy. But oil won't simply start flowing through the key shipping artery the way it did before the war. Then, it carried a fifth of the world's crude. Now, it will take time for hundreds of ships trapped in the Persian Gulf to exit through the narrow strait. And Gulf oil producers that throttled back production will need time to get oil moving again. And ship captains may take their time deciding it's safe and that the threat of attack from Iran has truly receded.