There is a direct flight from Vienna, the headquarters of the International Atomic Energy Agency (IAEA), to Teheran that takes about four hours and 20 minutes. Given that the Iranians first disclosed to the IAEA on September 21 their previously secret uranium enrichment plant at Fordu, near the holy city of Qom, it remains puzzling why its inspectors could not be on a plane within days to inspect the facility. The P-5+1 group, representing the US, Russia, France, Britain, China and Germany, gave the Iranians two weeks to open the enrichment plant. However, on October 2, the State Department spokesman, Ian Kelly, seemed to relax that demand when he said: "I don't think that there's a hard-and-fast deadline." He added: "I don't know that it's written in stone necessarily." The Iranians then managed to push the first inspection off to October 25, more than a month after the Fordu plant came to light. WHAT DOES timing matter with the Iranians? Back in March 2004, the IAEA was convinced there was incriminating evidence about the Iranian nuclear program at the Lavizan Technological Research center near Teheran. The Iranians managed to postpone the IAEA visit for about 30 days, and in the meantime they razed several buildings at the facility and even dug out two meters of the earth where they had previously stood in order to make it more difficult for inspectors to take soil samples that contained radioactive materials. By delaying the IAEA visit to Lavizan, the Iranian government concealed what its scientists were doing there. Teheran was off the hook from any crippling sanctions. Moreover, Lavizan was the location of the Iranian weaponization group which designed and constructed nuclear warheads. Former Israeli intelligence sources believe that the Iranians simply used the time they gained in dismantling Lavizan, after they were caught, and moved their weaponization work to another site. Time allowed Iran to not only cleanse Lavizan, but also to transfer valuable equipment elsewhere. There was an even longer delay for an IAEA inspection during the previous year, when the UN nuclear watchdog sought to inspect the Kalaye electric facility. The Iranians managed to get a delay from February to August 2003. In the meantime they retiled and repainted several suspected rooms before the IAEA teams arrived. Their purpose was to prevent the inspectors from obtaining any incriminating evidence from swipes of the walls that radioactive materials were ever present. Another Iranian technique was to permit the IAEA to take environmental samples near some buildings but not close to others; Teheran adopted this method when the IAEA came in 2005 to inspect, after yet another delay, the Parchin Military Complex, where conventional high explosives had been tested that could be used for detonating a nuclear device. Looking back at past precedents for inspections of suspected nuclear sites in Iran, it is clear that time matters, for the leadership in Teheran has a proven track record in exploiting time to its advantage every time there was a contest of wills with the West. GAINING TIME was clearly one of the purposes of Iran during its October 1 meeting in Geneva with the P-5+1. Prior to that meeting the Iranians were facing rising international pressures, that could have resulted in immediate, severe sanctions, after their Fordu enrichment plant came to light. There were reports that the Russians might join the West with new sanctions against Iran. Something had to be done to burst the balloon of pressure that Iran was facing. Besides delaying an IAEA inspection, the Iranians raised the possibility of transferring a portion of their inventory of low-enriched uranium outside of Iran to Russia, for further enrichment up to just within the maximum permitted civilian levels of U-235. The Western press largely praised this proposal as a groundbreaking act. But was there a solid agreement here? The UN secretary-general's spokesman, Michele Montas, called it a "nuclear fuel supply concept." He added that "the concept" will be discussed at a technical meeting at the IAEA on October 19. Who knows how much time will pass until the concept becomes a detailed agreement, if at all? The main point was that with a seemingly forthcoming proposal that may end with nothing, Iran was slipping off the hook in many important circles of international opinion. The main question is how all this activity will affect decision-making in the US Congress which is considering severe sanctions against Iran, including an embargo against gasoline imports to the Islamic republic. Since 2006, Iran has been defying at least five UN Security Council resolutions which call on it to halt all uranium enrichment. For that purpose, Congressman Howard Berman (D-Calif.), the chairman of the House Foreign Affairs Committee, and Rep. Ileana Ros-Lehtinen (R-Florida) have introduced the "Iran Refined Petroleum Sanctions Act." But will the bill be reported out of committee to the floor of the House of Representatives for a vote, while the post-Geneva discussions with Iran continue? There will be an effort to delay any Congressional action as long as the parties are talking. Meanwhile, the centrifuges in the main Iranian enrichment facility at Natanz will continue to spin, producing more enriched uranium and enlarging the potential arsenal of Iran's atomic weapons. HALTING A nuclear Iran is a very urgent matter. The disclosure of a clandestine uranium enrichment plant in September created a real sense of common purpose across the whole Western alliance. But Iran's diplomacy has managed to reverse that sense of urgency and reinvigorated the idea that the nuclear problem can be resolved by diplomatic engagement alone. And should Iran manage to rid itself by October 25 of any incriminating evidence at its Fordu enrichment plant near Qom, then it will be hard to motivate the West to take new action. As Iran succeeds in breaking every deadline that has been issued, its resolve only increases. It is still possible to avert Iran's last sprint to the nuclear finishing line. But it will require even greater determination on the side of the West, especially in Washington, to move forward on crippling sanctions. The world needs to recognize the truth: the regime in Teheran is seeking at all costs to achieve nuclear weapons. The Obama administration must let Congress move immediately to draw an economic line in the sand, that has not be drawn until now, and not wait for more negotiations until it is too late. The writer is the author of The Rise of Nuclear Iran: How Tehran Defies the West (Regnery, 2009). He is the President of the Jerusalem Center for Public Affairs and served as Israel's ambassador to the United Nations.