Better way for a timer to load a level?

Currently I’m using waitforseconds to delay my level loading controlled by a if statement if the score is a certain score per level, but what is happening is the coroutine is getting called like 10 or more times before that statement is false. I was thinking i could just replace waitforseconds with invoke, then do all i need to do to load the level in those functions but wouldn’t those get called like 10 or more times too if they are still in the update function? How would i go about getting a delay for the level to load while constantly checking the score and then only calling a invoke once or waitforseconds once? here is my current code. Thanks.

public static  ScoreBoard  global;
public static float Score = 0f;
public static float Lives = 3f;
public static bool lvlChange = false;
public static float Timer = 0;
public static bool countdown = false;
public GameObject spawnHolder;
public static bool Respawning = false;
public static bool wonGame = false;
//public static bool paddleDieLvlChange = false;
// Use this for initialization
void Start () {
//global=this;
}

// Update is called once per frame
void Update () {
    if (Application.loadedLevelName == "Level1" && Score >= 280) // should be 330
    {
        StartCoroutine(IntermissionL1());                        
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level2" && Score >= 360) // should be 360
    {
        StartCoroutine(IntermissionL2());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level3" && Score >= 370) // should be 440
    {
        StartCoroutine(IntermissionL3());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level4" && Score >= 430) // should be 430
    {
        StartCoroutine(IntermissionL4());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level5" && Score >= 530) // should be 530
    {
        StartCoroutine(IntermissionL5());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level6" && Score >= 470) // should be 470
    {
        StartCoroutine(IntermissionL6());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level7" && Score >= 280) // should be 280
    {
        StartCoroutine(IntermissionL7());
        Score = 0f;
    }

    if (Application.loadedLevelName == "Level8" && Score >= 340) // should be 340
    {
        StartCoroutine(IntermissionL8());
        Score = 0f;
    }

    if (Application.loadedLevelName == "YouWon") 
    {
        StartCoroutine(YouWon());
        wonGame = true;
        Score = 0f;
    }

    if (Lives == 0f)
    {
        Application.LoadLevel("GameOver");
        Score = 0f;
        Lives = 3f;
    }

    if (Ball_Movement.playerDead == true)
    {
        StartCoroutine(Countdown());
        
    }
    
    
}
// Makes a GUI from the variable score which needs to be tied to when a block dies.
void OnGUI()
{
    GUI.Box(new Rect(10, 430, 100, 20), "" + Score);
    GUI.Box(new Rect(350, 430, 100, 20), "" + Lives);
    if (countdown)
    {
        GUI.Box(new Rect(180, 400, 100, 20), "Respawning!!"); 

    }
    if (lvlChange)
    {
        GUI.Box(new Rect(40, 400, 500, 20), "You Won! Changing levels in 5 Seconds...");

    }

    if (wonGame)
    {
        GUI.Box(new Rect(40, 300, 300, 20), "You Beat the Whole Game WOOHOO!!!...");

    }
}
private IEnumerator Countdown()
{
    Ball_Movement.playerDead = false;
    countdown = true;
    yield return new WaitForSeconds(5f);
    countdown = false;
    RespawnPlayerAndBall();
}

private IEnumerator IntermissionL1()
{
    
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);       
    Application.LoadLevel("Level2");
    lvlChange = false;

}

private IEnumerator IntermissionL2()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);   
    Application.LoadLevel("Level3");
    lvlChange = false;

}

private IEnumerator IntermissionL3()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);   
    Application.LoadLevel("Level4");
    lvlChange = false;

}

private IEnumerator IntermissionL4()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);
    //Ball_Movement.playerDead = false;
    Application.LoadLevel("Level5");
    lvlChange = false;

}

private IEnumerator IntermissionL5()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);
    //Ball_Movement.playerDead = false;
    Application.LoadLevel("Level6");
    lvlChange = false;

}

private IEnumerator IntermissionL6()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);
    //Ball_Movement.playerDead = false;
    Application.LoadLevel("Level7");
    lvlChange = false;

}

private IEnumerator IntermissionL7()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);
    //Ball_Movement.playerDead = false;
    Application.LoadLevel("Level8");
    lvlChange = false;

}
private IEnumerator IntermissionL8()
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(5f);
    //Ball_Movement.playerDead = false;
    Application.LoadLevel("YouWon");
    lvlChange = false;

}

private IEnumerator YouWon()
{
    wonGame = true;
    yield return new WaitForSeconds(7f);
    Application.LoadLevel("Credits");
    wonGame = false;

}

void RespawnPlayerAndBall()
{
    GameObject paddleSpawn = (GameObject)Instantiate(spawnHolder, new Vector3(0, 1, -15), transform.rotation);
    Respawning=true;
}

}

You could (or should) use parameters instead of 8 equal coroutines. Your Intermission coroutine should look more like this:

private IEnumerator Intermission(string aLevel, float aDelay)
{
    Destroy(PaddleMove.Instance.gameObject);
    Destroy(Ball_Movement.instance.gameObject);
    lvlChange = true;
    yield return new WaitForSeconds(aDelay);
    Score = 0.0f;
    Application.LoadLevel(aLevel);
    lvlChange = false;
}

Also you have already your lvlChange variable which could be used in Update to not call the end levelchecks when a level change is already triggered.

Anyway, i would do it like this:

public string[] levels = new string[]
{
    "Level1",
    "Level2",
    "Level3",
    "Level4",
    "Level5",
    "Level6",
    "Level7",
    "Level8",
    "YouWon"
}
public float[] levelScores = new float[]
{
    280.0f,  // level 1
    360.0f,  // level 2
    370.0f,  // level 3
    430.0f,  // level 4
    530.0f,  // level 5
    470.0f,  // level 6
    280.0f,  // level 7
    340.0f,  // level 8
    0.0f     // end
}
public static int currentLevel = 0;
void Start()
{
    StartCoroutine(WinCheck());
}
IEnumerator WinCheck()
{
    while(true)
    {
        if (currentLevel < levels.Length-1)
        {
            if (Score >= levelScores[currentLevel])
            {
                currentLevel++;
                yield return Startcoroutine(Intermission(levels[currentLevel], 5.0f));
            }
        }
        else
        {
            yield return StartCoroutine(YouWon());
        }
        yield return null;
    }
}