The fact is that there is no hard and fast rule as how long law enfrocment can follow you before pulling you over. In other words, it is up to their discretion. They can choose to follow you for as long as it takes them to reasonably determine that you might pose a danger to the public safety. Therefore, as an example, they might follow someone who was driving recklessly or carelessly for a period of time in order to see if the driver commits any other traffic violations or may be engaged in some sort of criminal activity.