There absolutely is stuff you can do in that 12-hour window to preapare for a CME hitting earth.
Most apparent is the task of removing the sensitive components out of your car and protecting them.
Seems like a no brainer.
What are the sensitive components in my car? Mine is a 1996 Caravan, and my BF has a 2007 Honda Civic. Would it help to have a car in a garage?