It depends on your interpretation of "smooth".
Lerp offers a transition similar, but its a curve so the start, and end can be slower than the middle. Ease out, ease in if you will.
Also you cant really do exactly 6 seconds, nor should you expect that in a system that goes on frame rate.
However, if that's not terribly important, you can get a close approximation using dt.
I'd suggest some experimentation with variables as triggers if you absolutely have to that kind of precession.
Just be ready for frame skips.