"No matter what the spin from Time magazine's "man of the year", US President George W Bush, or defense chief Donald Rumsfeld, there's one overarching question facing the 83 entities - nine coalition lists, 47 political parties and 27 individuals, totaling more than 5,000 candidates - now competing for the 275 seats in Iraq's interim parliament and that will be entitled to write the next Iraqi constitution. The absolute majority of Iraqis want the Americans out of their country as soon as possible. But how?

The United Iraqi Alliance - the Shi'ite, Grand Ayatollah Ali al-Sistani-supervised electoral list (228 candidates) - has a detailed, 23-point platform. According to its main negotiator, Hussein Shahristani, the platform insists on the "sovereignty, unity and Islamic identity" of Iraq, and most crucially includes a plan with a precise date for the end of the military occupation. Whether the Americans will accept the plan (neo-conservative dreams for the Middle East collapsing in the sand), or whether this will be enough to placate Sunni anger, no one yet knows."
http://atimes.com/atimes/Middle_East/FL24Ak03.html

I think there is no question that if asked by the Soveriegn power of Iraq to leave Iraq, the US and the Coalition forces will be very responsive to the request. Politically and miltarily we couldn't sustain defying the will of the Iraqis, and the Grand Ayatollah Ali al-Sistani, by his stature alone, certainly has the influence to make us leave.
And there is no problem with Iraqi giving us a deadline- it's different dynamic than if we gave a deadline. If we gave a deadline, then it would be very hard to change the deadline [if situation required it], but if Iraq's soveriegn authority gave a deadline, then they could change/modify it fairly easily- if they deemed it neccessary (it's a pretty good assumption that if we agreed that the Coalition forces were actually needed to be extended that we would agree to a change).