Question smooth change SkyBox

I need to smoothly change the SkyBox to another one, I found an example on the net, all the examples are the same, I made the same one for myself

Code (CSharp):

1. if(t < 1f){
2.     Debug.Log("t => " + t);
3.     t += 0.5f * Time.fixedDeltaTime;
4.     if(t >= 1f){ t = 1f; }
5.     RenderSettings.skybox.Lerp(OldSkyBox, NewSkyBox, t);
6.     }

but it changes sharp, what could be wrong?