how did they not notice michael driving behind them

For hours? Just because the sun goes down while they're driving and it's dark when they reach their destination doesn't mean they drove for hours.

It's October 31st. It goes from dusk to dark in minutes.

What tunes was Michael listening to on the car radio? Maybe some late 70s Stones: "Miss You" or "Beast of Burden"?

Annie was high and she was the driver.