If you leave early, you can take your time. You can pack your car with greater leisure and escape with everything you want to your first choice location, or have your pick of available shelters from aid agencies. It will give you time to settle yourself and your pets. Leaving early may also reduce the sense of panic that can come with a hurried departure.
Yet, if you leave too early, you may use up the valuable resources in your emergency kit. It will also make you dependent upon shelters and your savings, depleting your personal resources unnecessarily. Extended time away from your home can also put it at risk for days before a fire arrives.
The key to knowing when to leave so that you can be gone before gridlock and panic set in is not waiting until the official word comes through to run for safety. With everyone getting the message at the same time, it creates panic. For a prepared family, leaving beforehand will ensure a smoother departure and the pick of shelters and resources.