You don’t have to set everything to pass for 7 seconds, but if you have something that you want the viewer to see clearly, that is pretty much the minimum. For anything going faster, you will have to use so much motion blur to make it smooth it will definitely be very blurry. You can (and indeed should) have object that create parallax, just that it is better make them “unimportant” objects, such as telephone poles and other things that don’t matter if they are not in sharp focus.
Since it seems your preference is clarity over motion, I would definitely go this way.
If you were trying to show fast motion, rather than having text that the viewer is expected to be able to read and other details you rather keep sharp, you could have the picture pass the frame in half a second with extreme motion blur and it could still look “smooth”, just that you wouldn’t be able to tell exactly what there is in the image.
So it is not a rule for all situations, more of a good general guideline for panning motion.