erratic movement when rotating an arbitrary point around another arbitrary point

I have written the following methods to rotate an arbitrary point around another arbitrary point by an angle over a duration. The point in question now moves erratically, but ends up around where I believe is the desired destination. I need to get it to move smoothly to the angle.

Please note that the points are independent of a game object.

From the diagram below, I am trying to move one point of a bezier curve (drawn with a LineRenderer) around another point by an angle over a given period of time. None of these points coincide with the position of the game object which contains the bezier curve. 


Code (CSharp):

1. IEnumerator runMovement()  {
2.  
3.     yield return new WaitForSeconds(2.0f);
4.     Vector2 pivot = points[3];
5.  
6.     StartCoroutine(RotateControlPointWithDuration(pivot, 2.0f, 90.0f));
7.  
8. }
9.  
10.    IEnumerator RotateControlPointWithDuration(Vector2 pivot, float duration, float angle)
11. {
12.     float currentTime = 0.0f;
13.     float ourTimeDelta = 0;
14.     Vector2 startPos = points[0];
15.  
16.     ourTimeDelta = Time.deltaTime;
17.     float angleDelta = angle / duration; //how many degress to rotate in one second
18.  
19.     while (currentTime < duration)
20.     {
21.         currentTime += Time.deltaTime;
22.         ourTimeDelta = Time.deltaTime;
23.  
24.         points[0] = new Vector2(Mathf.Cos(angleDelta * ourTimeDelta) * (startPos.x - pivot.x) - Mathf.Sin(angleDelta * ourTimeDelta) * (startPos.y - pivot.y) + pivot.x,
25.                                                         Mathf.Sin(angleDelta * ourTimeDelta) * (startPos.x - pivot.x) + Mathf.Cos(angleDelta * ourTimeDelta) * (startPos.y - pivot.y) + pivot.y);
26.  
27.         yield return null;
28.     }
29. }