SCOTUS has ruled that you can not be detained longer than is reasonable to conduct the traffic stop for which you were pulled over for. You cannot be detained one second longer because of some suspicion that has no basis in reasonable, articulable suspicion that an actual crime has been committed or is about to be committed.
See Rodriguez v. United States
Exactly what I was referring to.
But the cops are not going to tell you that
You can voluntarily stay and talk to the police as long as you like and most people will do just that because they don’t know that they are free to leave.