How do I add a timer /wait time & limiter for Spawning?

Hi Guys,

 var enemySlot: GameObject;
 var spawn1 : GameObject;
 var spawn2 : GameObject;
 var spawnTime = 70.0;
 var Xenemies : int; // to define how many enemies i wish to clone in each 
                     //spawn period

 function Update () 
 {
     InvokeRepeating("spawn", .01, spawnTime);
 }
 
 function spawn()    
 {    
     var time : int = Time.realtimeSinceStartup * 1000;    
     if((time & 0x01) == 0) //Checking if the time millisecond count is an even number(To make it come out of random side)    
     {    
         Instantiate(enemySlot, spawn1.transform.position,  Quaternion.identity); 
         Debug.Log("spawn1 enemy created"); 
         //yield WaitForSeconds(3);      
     }    
     else    
     {    
         Instantiate(enemySlot, spawn2.transform.position,  Quaternion.identity);
         Debug.Log("spawn2 enemy created");  
     }    
 }

I tried using the InvokeRepeating, but it still clone too many.

1) How do i add a timer or wait time to the code, so it will like every 3 sec then it will clone X enemies.

2) Where & how should i put my Xenemies in the code, so i can define like each Spawn execution, clone X number of enemies.

3) and how should I actually use the InvokeRepeating in this case to help my game?

Thanks in advance!