Washington War has been declared. The world has been told to choose sides. So now the countdown begins.
Yet President Bush's thundering pledge Thursday night that "the hour is coming when America will act" offered not a single solid clue about just when that hour will be. Is the first strike just days away, as the Washington rumor mill has hyped it? Or is the United States in for a methodical Gulf War-type buildup of weeks or months to prepare for a major offensive?
Both possibilities have strengths and vulnerabilities, according to military and policy experts.
"If we intend to do some real disruption to the al-Qaida organization or even try to pick up Osama bin Laden, we'll need a lot of planning and preparation. On the other hand, the element of short-term surprise can be important," said Stephen Flanagan, director of Institute for National Strategic Studies at the National Defense University in Washington.
The calculations range from mundane but crucial factors such as weather the frigid winter snows usually freeze Afghanistan's civil war in place until the spring to religious considerations such as Ramadan, the Islamic month of fasting. Both begin in mid-November.
But the biggest issue in deciding when to attack is the military objective, analysts say. And that remains unclear.
Bush stressed Thursday that the ruling Taliban would be punished if it did not turn over bin Laden. But the big question he didn't answer was whether the United States actually intends to oust the Afghan government an issue the White House again refused to address Friday. The answer is all-important in determining when and how the first strike will take place.
"If you want to dislodge the regime in Kabul, you need an overwhelming ground force, which requires a good bit of time for deployment. If you want to punish them, then you can use a smaller package of special forces and air power more quickly put in place," said James Steinberg, deputy national security adviser during the Clinton administration, now at the Brookings Institution.
So far, with the deployment of dozens of military aircraft and untold special forces, the deployment appears limited by comparison to the 1991 Gulf War when 500,000 foreign troops fought in the U.S.-led coalition. That may indicate that the mission has narrower goals, analysts say.
"The emphasis is on special forces and long-term bombing with no apparent interest in repeating the Russian model," said Anthony Cordesman, a military strategist at the Center for Strategic and International Studies, referring to the 1979-89 Soviet occupation of Afghanistan.
The weather, meanwhile, argues for quick action and so do domestic and international politics.
"In the winter it'll be very difficult to put special forces on the ground and operate, so the preference would be to get as much as possible done before then," said Ken Pollack, a former Clinton and Bush National Security Council staffer now at the Council on Foreign Relations.
"The smart thing to do is wait until spring when you'd have tons of intelligence, forces set in place and ready to go and eight months of uninterrupted good weather to run an operation. But it's unclear whether domestic and international politics would sustain such a long wait."
By spring, the United States could also provide the Northern Alliance, the Afghan opposition force, with new supplies and training.
Once the bigger objective is determined, the precise day of attack will be driven almost entirely by intelligence that pinpoints where bin Laden and his fighters are, according to retired Marine Lt. Gen. Anthony Zinni, the last commander of U.S. forces in the Mideast.