how to start InvokeRepeating function and timer at the same time?

I am instantiating prefab randomly using InvokeRepeating in my scene and i have also timer like this float timeRemaining = 30.0f;. I want when InvokeRepeating function start then timer should start.
here is Invokereapeating

void Start () {
	InvokeRepeating ("SpawnObject", 3, 1);
}

And here is Timer function

void Update()
{
	//if (InvokeFunction.timerStarted == true) {
	if (timeRemaining > 0) {
		timeRemaining -= Time.deltaTime;
		time.text = "Time: " + System.Convert.ToInt32 (timeRemaining);
	}
	if (timeRemaining <= 0) {
		GameOver();
	}
	//	}
}

Please help me.
Thanks

Introduce additional variable, indicating if timer already started, and initialize it at the end of SpawnObject method (if not already initialized). Sample (might contain some typos, but general idea remains):

private bool timerStarted = false;

private void SpawnObject()
{
    // your spawn code

    if(!timerStarted)
    {
        timerStarted = true;
        timeRemaining = 10;
    }
}

void Update()
{
    if(timerStarted)
    {
        if (timeRemaining > 0)
        {
            timeRemaining -= Time.deltaTime;
            time.text = "Time: " + System.Convert.ToInt32 (timeRemaining);
        }
        else
        {
            GameOver();
        }
    }
}

public float timer = 0.0f;

void Update () 
	{
		timer += Time.deltaTime;

		if(timer > 30.0f)
		{
			GameOver();
			timer = 0.0f;
		}
	}

No need to include any additional variables.
This will work 100% as i have used this code in my project as well.

Since you are using the start function, your invokerepeating method starts when script is enabled. Simply change your start function into something else and call SomethingElse(); when you start your timer.

 void SomethingElse() {
     InvokeRepeating ("SpawnObject", 0, 1);
 }