I don't think there is any law, it's just the logic that it takes around six weeks for any surgical wound to heal properly.
Having said that, I drove when Immy and Maddy were two weeks old and started driving after this caesar about a week after because I had to go back and forth to the NICU. I think I drove myself home after Lily's caesar!!!
Of course, with William it was a different story, bigger surgery, different circumstances and didn't drive the car for about 3 months afterwards.