It would be a mistake to have given Saddam a deadline without already having a full attack plan at the ready...even well in advance...and have practiced it to the extent that it could be done so without revealing details. One does not threaten military action and then figure out how to accomplish it. GW had also made it known that full UN cooperation was desired but not an imperative in his decision making. Nothing is new in a story claiming that a memo was seen. Such reduces the piece to the credibility of the tabloids, IMO.
Then you make a plan how to get there.
Bush-Blair Iraq war memo revealed
The New York Times says it has seen a memo which shows that the US president was firmly set on the path to war two months before the 2003 Iraq invasion.
From private talks between George Bush and UK PM Tony Blair, the memo makes it clear the US was determined to go to war whether or not he had UN backing.
He is quoted discussing ways to provoke Saddam Hussein into a confrontation.