im running the following inside a Coroutine

//startRotation and endRotation are cached rotations from two different Transforms
var t = 0;
while(t < rotationDuration) {
    yield return null;
    t += Time.deltaTime;
    mRoot.rotation = Quaternion.Slerp(startRotation, endRotation, Time.time * 5f);
}

mRoot.rotation = mPath.rotationEnd.rotation;

which works fine for the rotation itself. Now I tried to do the rotation "over time" using this

//this is calculated before the while() loop
var angle = Quaternion.Angle(startRotation, endRotation) ;
var rate = angle / rotationDuration;

and plugging this into the Slerp function in this way.

mRoot.rotation = Quaternion.Slerp(startRotation, endRotation, Time.deltaTime * rate);

but all I get on the GO to be rotated is a jitter, no actual rotation. Any pointers in the right direction would be appreciated.