Timer reset

Hey guys, I have a timer in my game which should count the time till the end of the game. I can't figure out how to make it so it will only reset back to 0 when menu scene is active. ( build index 0) The second problem is that I don't want it to go back to 0 after every death(scene reload). Have you got any sugestions?

using UnityEngine; using UnityEngine.UI; using UnityEngine.SceneManagement;

public class Timer : MonoBehaviour { public Text TimerText; public bool shouldCountTime; public float t;

 private void Start()
 {
     if (SceneManager.GetActiveScene().buildIndex != 0)
     {
         shouldCountTime = true;
     }
     else
     {
         shouldCountTime = false;
         t = 0;
     }
     t = Time.deltaTime;
 }

 void Update()
 {
     if (shouldCountTime) {
         t += Time.deltaTime;
     }
     string minutes = ((int)t / 60).ToString();
     string seconds = (t % 60).ToString("f2");
     TimerText.text = minutes + ":" + seconds;
 } 

}