Tiznit is lively enough, but it is a young city, even if itís constructed after old patterns. The old city (or the not-so-young part of the city) is modernistic in a way. There are few ornaments, the walls are straight, and everything seems a little bit too proper.
The newer part of the city, which is outside the city walls, is the more vibrant one. And in night time, movements of people and colours make it very exotic, and this is of course the time to hang around, just to see what happens. Nothing harmful will happen to you, of course.