We have two different conversations about constitutional law. One is this hyper-technical purely legal analysis you see from lawyers and judges. The other is what really happens. So in this case, hooray, there are limits on the length of traffic stops, according to the USSC. But the other conversation says that if you get assertive about your constitutional rights in a real traffic stop, they won't let you go. Instead, you might get beaten, tazed, or shot. The cop will likely face no consequences, just by claiming you resisted, or posed a "threat," or "he reached for his waistband." None of it needs to be true because a "reasonable mistake" is good enough. So, what good are rights if cops don't respect them and get away with violating them, day in and day out? The technological fix being proposed is video--dash cams and body cameras--and that may help, but the overriding problem is that police are drunk with power in this country. They can get away with almost anything and they know it. The can manipulate the on-the-scene situation, they investigate themselves, they have the union and prosecutors and most judges on their side, and they are professional witnesses. Until that power situation changes, I think these USSC pronouncements are only meaningful in a small number of cases that get fully litigated. For thousands of day to day interactions between citizens and police, these "big decisions" are largely irrelevant.
http://www.scotusblog.com/2015/04/opinion-analysis-traffic-stops-cant-last-too-long-or-go-too-far-and-no-extra-dog-sniffs/