In the same time, I'm not actually advocating using time as reference because it would imply providing an update loop.
Instead, I'm advocating providing tools to quickly setup your own tweening by calling some system regularly with an update of where between the beginning 0 and the end 1 of the animation (this is the general term for this) the generated/animated values should be.
That way, it would be easier to setup tweening for your specific context of use of SFML (which carefully avoid providing a framework but just provide building blocks).