I agree that if you wait too long then getting on the road is pretty much certain death for anything but a well-armed and disciplined convoy. At the same time if you remain in an urban area or close in suburban area a single family in traditional housing WILL be dead/ raped/robbed in 10-30 days. A typical family home is simply indefensible and the zombies will come.
Any father who keeps his family in their suburban home is ordering his wife and children to die in place defending it. Or soon starve. IMHO.
How did you determine this?
I must confess, this statement reminded me of Michael Crichton's famous evaluation of the Drake Equation: what use is an equation whose variables are totally unknown, and can be anything from zero to infinity?