It will likely take at least two to three decades.
Although there is reason to believe that more than 50% of new cars will be electric by 2030, the average lifespan of passenger vehicles in the US is approximately 15 years. Even if/when all new cars are EV, it will still take some time for fossil-burners to reach their end of lives. Many people cannot afford to throw away their current vehicle. It could take two to three decades for fossil burners to become rare.