The explanation, as reported on BBC http://news.bbc.co.uk/2/hi/middle_east/3090639.stm and CNN.com and every other outlet I've seen is that delaying would have allowed the surrounding neigborhood to be flooded with a scene reminiscent of the neighborhood in the blocks outside the bank in the classic, "Dog Day Afternoon."
And, given, the depth of resistance to the occupation, organized and ad-hoc w/o connections to former Iraqi regime and foreign jihadists and pan-Arab nationalists, unless you think that the US military high command is just salivating for a My Lai massacre, the massing of armed crowds outside this villa, would have set of a real mass slaughter.
(BTW, Read some of the pig doctrine. "Asymmetrical Warfare: Today's Challenge to US Military Power, " by Roger W. Barnett. amazon.com review>"The Curtis Lemay Handbook for Squishing Mosquitoes with Multiple Nuclear Bombs" Lawrence Freedman, as befits his rep and where this review was is more restrained.... http://www.foreignaffairs.org/20030501fabook11240/roger-barnett/asymmetrical-warfare-today-s-challenge-to-u-s-military-power.html
Chronology: How the Mosul raid unfolded
The US military in Iraq has given a blow-by-blow account of the operation which it says resulted in the deaths of Saddam Hussein's sons Qusay and Uday. BBC News Online looks at the key moments. <SNIP> click the bbc url above