Production starts tomorrow morning. If there are no quality holds and they leave the factory without delay, then they should start hitting dealer lots by mid-March. If, however, Ford holds them up for quality control inspections (as they often do with new model introductions) then it may be April before they start arriving at the dealerships.
I have several 2010 Mustangs that I've ordered that currently show ETA's for the week of March 16th, if that helps give you any idea, though.