c# - How to make something rotate a certain amount over an exact amount of time

I'm trying to make a plane rotate down a certain amount and 180 degrees horizontally over 2 seconds.

Basically I want it to take the plane 1 second to rotate to a horizontal-facing angle, then take the other second to rotate 180 degrees around to face the other direction.

The formula I'm currently using is:

    //If you're rotating, lower the speed and rotate the plane.
    if (rotate == 1 && rotationPhase > 0) {
        //If in phase 0, figure out which phase you need too go to.
        if (angle > 90 && rotationPhase == 1) {

            //Rotation phase 2 = rotating down
            rotationPhase = 2;
            rotationAngleTime = angle - 90;
        }
        else if (rotationPhase == 1) {
            //Rotation phase 3 = rotating up
            rotationPhase = 3;
            rotationAngleTime = 90 - angle;
        }


        //After phase 0, if in phase 1 begin rotating down, if in phase 2 begin rotating up.
        if (angle > 90 && rotationPhase == 2) {
            transform.Rotate(0, 0, -rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)));
            angle -= rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (angle > 89 && angle < 91) {
                angle = 90;
                rotationPhase = 4;
                rotationAngleTime = 180;
            }
        }

        else if (rotationPhase == 3) {
            transform.Rotate(0, 0, rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)));
            angle += rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (angle > 89 && angle < 91) {
                angle = 90;
                rotationPhase = 4;
                rotationAngleTime = 180;
            }
        }


        //After you have rotated to horizontal in phase 1/2, rotate around to face the other direction.
        if (rotationPhase == 4) {
            transform.Rotate(rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)), 0, 0);
            rotationAngle += rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (rotationAngle > 179) {
                rotationAngle = 0;
                rotationPhase = 0;
                rotationAngleTime = 0;
            }
        }

    }

I've tried many different things, but I can't figure out what to do.

EDIT: This seems to be a problem with Time.deltaTime. I can get the plane to rotate correctly, but for some reason it's not rotating over the right amount of time. I have a timer being subtracted by Time.deltaTime, and this animation happening, and the animation always finishes about half a second before the timer runs out.

Answer

EDIT: This makes the animation run properly, but it's still not running at the correct amount of time.

I figured out how to fix the problem myself, the solution was:

//If you're rotating, lower the speed and rotate the plane.
    if (rotate == 1 && rotationPhase > 0) {
        //If in phase 0, figure out which phase you need too go to.

        if (angle > 90 && rotationPhase == 1) {
            //Rotation phase 2 = rotating down
            rotationPhase = 2;
            rotationAngleTime = angle - 90;
        }
        else if (rotationPhase == 1) {
            //Rotation phase 3 = rotating up
            rotationPhase = 3;
            rotationAngleTime = 90 - angle;
        }


        //After phase 0, if in phase 1 begin rotating down, if in phase 2 begin rotating up.
        if (angle > 90 && rotationPhase == 2) {
            transform.Rotate(0, 0, -rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)));
            angle -= rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (angle > 89 && angle < 91) {
                angle = 90;
                rotationPhase = 4;
                rotationAngleTime = 180;
            }

        }
        else if (rotationPhase == 3) {
            transform.Rotate(0, 0, rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)));
            angle += rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (angle > 89 && angle < 91) {
                angle = 90;
                rotationPhase = 4;
                rotationAngleTime = 180;
            }
        }


        //After you have rotated to horizontal in phase 1/2, rotate around to face the other direction.
        if (rotationPhase == 4) {
            transform.Rotate(rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2)), 0, 0);
            rotationAngle += rotationAngleTime * (Time.deltaTime * (rotationSpeed / 2));
            if (rotationAngle > 179) {
                rotationAngle = 0;
                rotationPhase = 0;
                rotationAngleTime = 0;
            }

        }
    }