Projectile destruction when time reaches zero

I'm making a fps and want enemy projectiles to stop shooting around the last 1 one second of the round so the rigidbody does not activate "play again" buttons at time over. I do have a timer attached to my game manager but I'm having trouble referencing it my projectile shooting script. Is there a way I can change my code to create this reference.

Game Manager

 public class GameManager : MonoBehaviour {
 
     // make game manager public static so can access this from other scripts
     public static GameManager gm;
 
     // public variables
     public int score=0;
 
     public bool canBeatLevel = false;
     public int beatLevelScore=0;
 
     public float startTime=5.0f;
     
     public Text mainScoreDisplay;
     public Text mainTimerDisplay;
 
     public GameObject gameOverScoreOutline;
 
     public AudioSource musicAudioSource;
 
     public bool gameIsOver = false;
 
     public GameObject playAgainButtons;
     public string playAgainLevelToLoad;
 
     public GameObject nextLevelButtons;
     public string nextLevelToLoad;
 
     public float currentTime;
 
     // setup the game
     void Start () {
 
         // set the current time to the startTime specified
         currentTime = startTime;
 
         // get a reference to the GameManager component for use by other scripts
         if (gm == null) 
             gm = this.gameObject.GetComponent<GameManager>();
 
         // init scoreboard to 0
         mainScoreDisplay.text = "0";
 
         // inactivate the gameOverScoreOutline gameObject, if it is set
         if (gameOverScoreOutline)
             gameOverScoreOutline.SetActive (false);
 
         // inactivate the playAgainButtons gameObject, if it is set
         if (playAgainButtons)
             playAgainButtons.SetActive (false);
 
         // inactivate the nextLevelButtons gameObject, if it is set
         if (nextLevelButtons)
             nextLevelButtons.SetActive (false);
     }
 
     // this is the main game event loop
     void Update () {
         if (!gameIsOver) {
             if (canBeatLevel && (score >= beatLevelScore)) {  // check to see if beat game
                 BeatLevel ();
             } else if (currentTime < 0) { // check to see if timer has run out
                 EndGame ();
             } else { // game playing state, so update the timer
                 currentTime -= Time.deltaTime;
                 mainTimerDisplay.text = currentTime.ToString ("0.00");                
             }
         }
     }
 
     void EndGame() {
         // game is over
         gameIsOver = true;
 
         // repurpose the timer to display a message to the player
         mainTimerDisplay.text = "GAME OVER";
 
         // activate the gameOverScoreOutline gameObject, if it is set 
         if (gameOverScoreOutline)
             gameOverScoreOutline.SetActive (true);
     
         // activate the playAgainButtons gameObject, if it is set 
         if (playAgainButtons)
             playAgainButtons.SetActive (true);
 
         // reduce the pitch of the background music, if it is set 
         if (musicAudioSource)
             musicAudioSource.pitch = 0.5f; // slow down the music
     }
     
     void BeatLevel() {
         // game is over
         gameIsOver = true;
 
         // repurpose the timer to display a message to the player
         mainTimerDisplay.text = "LEVEL COMPLETE";
 
         // activate the gameOverScoreOutline gameObject, if it is set 
         if (gameOverScoreOutline)
             gameOverScoreOutline.SetActive (true);
 
         // activate the nextLevelButtons gameObject, if it is set 
         if (nextLevelButtons)
             nextLevelButtons.SetActive (true);
         
         // reduce the pitch of the background music, if it is set 
         if (musicAudioSource)
             musicAudioSource.pitch = 0.5f; // slow down the music
     }
 
     // public function that can be called to update the score or time
     public void targetHit (int scoreAmount, float timeAmount)
     {
         // increase the score by the scoreAmount and update the text UI
         score += scoreAmount;
         mainScoreDisplay.text = score.ToString ();
         
         // increase the time by the timeAmount
         currentTime += timeAmount;
         
         // don't let it go negative
         if (currentTime < 0)
             currentTime = 0.0f;
 
         // update the text UI
         mainTimerDisplay.text = currentTime.ToString ("0.00");
     }
 
     // public function that can be called to restart the game
     public void RestartGame ()
     {
         // we are just loading a scene (or reloading this scene)
         // which is an easy way to restart the level
         Application.LoadLevel (playAgainLevelToLoad);
     }
 
     // public function that can be called to go to the next level of the game
     public void NextLevel ()
     {
         // we are just loading the specified next level (scene)
         Application.LoadLevel (nextLevelToLoad);
     }
     
 
 }

Projectile Firing script

 public class EnemyProjectile : MonoBehaviour
 {
 
     public Rigidbody projectile;
     public float bulletsPerSecond = 0.5f;
     public float bulletImpulse = 20.0f;
 
     private bool shooting = false;
 
     // Use this for initialization
     void Start()
     {
         InvokeRepeating("Shoot", 0.0f, 1.0f / bulletsPerSecond);
     }
 
     void Shoot()
     {
         if (shooting = true)
         {
             Rigidbody bullet = (Rigidbody)Instantiate(projectile, transform.position + transform.forward, transform.rotation);
             bullet.AddForce(transform.forward * bulletImpulse, ForceMode.Impulse);
         }
     }
 
     // Update is called once per frame
     void Update()
     {
         RaycastHit hit;
         if (Physics.Raycast(transform.position, transform.forward, out hit))
         {
             if (hit.collider.gameObject.tag == "Player")
             {
                 if (EnemyAI.isAlive)
                 {
                     shooting = true;
 
                 }
             }
         }
     }
 }

Thanks for any help in advance, this is my first project ive coded in C# any other suggestions are welcome.