How to display ads every 5 mins ?

I am using ADmob ads, here is my script:

 public static AdManager Instance{set;get;}
 public string bannerId;
 public string videoId;
 private void Start()
 {
     Instance = this;
     DontDestroyOnLoad (gameObject);
     #if UNITY_EDITOR
     #elif UNITY_ANDROID
     Admob.Instance ().initAdmob (bannerId,videoId);
     Admob.Instance ().loadInterstitial ();
     #endif
 }
 public void ShowBanner()
 {
     #if UNITY_EDITOR
         Debug.Log("Unable to play banner ads from EDITOR");
     #elif UNITY_ANDROID
     Admob.Instance().showBannerRelative (AdSize.Banner, AdPosition.BOTTOM_CENTER, 5);
     #endif
 }
 public void ShowVideo()
 {
 #if UNITY_EDITOR
     Debug.Log("Unable to play ads from EDITOR");
 #elif UNITY_ANDROID
     if (Admob.Instance ().isInterstitialReady ()) 
     {
         Admob.Instance ().showInterstitial ();
     }
 #endif
 }

You want to use InvokeRepeating.