Start and Stop Timer Help

My code is a little messed up, the timer works but I need to add a start and stop button?

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class timer : MonoBehaviour {

	private static timer _instance ;

	public Text timerLabel;
	
	private float time;

	/*void Awake() {
		DontDestroyOnLoad(transform.gameObject);
	}*/

	//Begin New
	void Awake()
	{
		//if we don't have an [_instance] set yet
		if(!_instance)
			_instance = this ;
		//otherwise, if we do, kill this thing
		else
			Destroy(this.gameObject) ;
		
		
		DontDestroyOnLoad(this.gameObject) ;
	}
	//End New
	
	void Update() {

		
		time += Time.deltaTime;

		var minutes = Mathf.Floor(time / 60);
		var seconds = time % 60;//Use the euclidean division for the seconds.
		var fraction = (time * 100) % 100;
		
		//update the label value
		timerLabel.text = string.Format ("{0:00} : {1:00} : {2:00}", minutes, seconds, fraction);
	}

	//Reset Timer
	public void  ResetTimer(){
		time = 0;
		Debug.Log("Timer Reset");
	}

	//Stop Timer
	public void  StopTimer(){
		//Stop Timer Here

		Debug.Log("Timer Stopped");
	}
}

Add a bool pauseTimer and an if statment on line 35 make it

If(!pauseTimer)
    time += time.deltaTime;

Now when you set this bool to true the time variable will not be incremented