slower LookAt function

i have 2 object, cube and target and i want script for slow cube rotation to the target
i already create something but it not working as i want

Vector3 CubeVector = Cube.rotation *; // Vector3 of cube
vector3 targetVector = targetobject.rotation*;
if (CubeVector != targetVector )
	rotationSpeed = 0.005f; // this should slow rotation to target

    CubeVector = (CubeVector + (CubeVector -   targetVector )*rotSpeed);
  Debug.Log(CubeVector );

but this is not working as i want :confused:
can someone give me an advice pls ?

Multiply the 0.0005f value by Time.deltaTime()