How should I code a basic timer script in C#?

So I am trying to make an object move backwards in C#:

void Update () {

transform.Translate(Vector3.back * Time.deltaTime, Space.World);

}

However, I only want it to move backwards for a certain amount of time. How would I go about this? BTW I am a massive newbie with this stuff if you couldn’t already tell.

Here you go, please read the comments:

C#:

float timeLimit = 10.0f; // 10 seconds.
void Update()
{
	// translate object for 10 seconds.
	if(timeLimit > 1) {
		// Decrease timeLimit.
		timeLimit -= Time.deltaTime;
		// translate backward.
		transform.Translate(Vector3.back * Time.deltaTime, Space.World);
		Debug.Log(timeLimit);
	}
}

Javascript:

var timeLimit : float = 10.0f; // 10 seconds.
function Update()
{
	// translate object for 10 seconds.
	if(timeLimit > 1){
		// Decrease timeLimit.
		timeLimit -= Time.deltaTime;
		// translate backward.
		transform.Translate(Vector3.back * Time.deltaTime, Space.World);
		Debug.Log(timeLimit);
	}
}