Before Thursday night's dramatic vote at the UN security council, European diplomats were saying that resolution 1973, and the sweeping military measures it authorises in Libya, could be put into effect "in hours".

Just how many hours it will take is critical to the rebel stronghold of Benghazi which is braced for an attack from forces loyal to Muammar Gaddafi. The Libyan leader warned that his troops would go from house to house and room to room when they took the city, showing "no mercy". The onslaught did not materialise on Thursday night as Gaddafi had threatened, but government forces have massed in preparation for an attack, so it clear that if the Security Council words are to mean anything, time is very short.

If this had been a Bush-era "coalition of the willing" operation, it could have been put into action quite rapidly. The US would have done all the fighting with a few token British and French planes along for company. But the Obama administration, which tried very hard to avoid this moment, is insistent that the Arabs and Europeans must at least be seen to take the lead, and that will take more time. There is a trade-off between speed and making it look right.

First of all, the matter has to go to Nato, where contingency planning has been underway for a couple of weeks, but where Turkey has been resisting military intervention. Any decision to act requires unanimity.

If and when that resistance is overcome, it is likely that the Nato air base at Sigonella in Sicily will become the hub for operations, supported by French and British bases around the Mediterranean. Then it will be a question of assembling all the fighter jets, the refuelling planes, the surveillance, search-and-rescue, and electronic warfare aircraft necessary to mount a campaign.