How long can police hold me on the side of the road?

There's no clock in the statute. The measure is the mission — a stop may last as long as it reasonably takes to address the reason for it and attend to related safety concerns.

For a routine traffic stop, that means checking the license and registration, running the driver, and issuing a citation or warning. When that's complete, the justification for detaining you ends.

What doesn't extend the stop lawfully: unrelated questioning that prolongs it, waiting for a K-9 unit after the mission is finished, or holding someone while officers develop suspicion they didn't have when they pulled over.

What can extend it: new facts arising during the stop that create independent reasonable suspicion of something else.

In practice, most challenges here are arithmetic. How long did the stop actually take, when was the citation complete, and what was happening during the gap between the two.