How to create Count Down Timer in Unity

Notes:

How to create Count Down Timer in Unity:

using UnityEngine;
using UnityEngine.UI;
public class TimerController : MonoBehaviour {

Text timerText;
public int maxLevelPlayTime;
int timeLeft;

void Start () {
timerText = this.GetComponent<Text>();
timeLeft = maxLevelPlayTime;
timerText.text = "Time Left:" + timeLeft;
}

void Update () {
if (timeLeft > 0) {
timeLeft = (int)(maxLevelPlayTime - Time.timeSinceLevelLoad);
timerText.text = "Time Left:" + timeLeft;
}
}
}