unity3d - How to select a UI button based on a time triggered gaze input using GVr and unity? -

i using unity5 , gvr.i trying implement menu user stares @ button 5secs button enabled.can please me? have implemented reticle , detects button.i not sure how , should add time trigger.

attach script button object:

[requirecomponent(typeof(button))] public class interactiveitem : monobehaviour, ipointerenterhandler, ipointerexithandler {     public image progressimage; // add image child button object , set image type filled. assign field in inspector.     public bool isentered = false;     recttransform rt;     button _button;     float timeelapsed;     image cursor;     // use initialization     void awake ()      {         _button = getcomponent<button>();         rt = getcomponent<recttransform>();      }      float gazeactivationtime = 3;      void update ()      {         if(isentered)         {             timeelapsed += time.deltatime;             progressimage.fillamount = mathf.clamp(timeelapsed/gazeactivationtime,0,1);             if(timeelapsed >= gazeactivationtime)             {                 timeelapsed = 0;                 _button.onclick.invoke();                 progressimage.fillamount = 0;                 isentered = false;             }         }         else         {             timeelapsed = 0;         }     }      #region ipointerenterhandler implementation      public void onpointerenter (pointereventdata eventdata)     {         isentered = true;     }      #endregion      #region ipointerexithandler implementation      public void onpointerexit (pointereventdata eventdata)     {         isentered = false;         progressimage.fillamount = 0;     }     #endregion