Spawning Creatures

I'm trying to figure out a spawn code and I just got lost. I'm trying to set a spawn timer but it doesn't work. My script just spawns all 10 creatures at the same time. Can you help me with that?

Here is my code:

 using UnityEngine;
 using System.Collections;
 
 public class Spawn : MonoBehaviour 
 {
     public GameObject monsterPrefab; // Set this in inspector to the monster prefab.
 
     public int count = 0;
 
     private float timeSinceLastSpawn = 0;
 
     GameObject monsterInstance;
     Transform[] spawnpoints;
 
 
     void Update()
     {
         spawnpoints = GetComponentsInChildren<Transform>();
         while (count<10)
         {
             if (timeSinceLastSpawn <= 0)
             {
                 Spawner();
                 timeSinceLastSpawn = 4;
                 count++;
             }
             timeSinceLastSpawn -= Time.deltaTime; 
         }
         Debug.Log(timeSinceLastSpawn);
     }
 
     void Spawner()
     {
         int index = Random.Range(0, spawnpoints.Length - 1);
         var spawnpoint = spawnpoints[index];
         monsterInstance = (GameObject)Instantiate(monsterPrefab,
                                                   spawnpoint.position,
                                                   spawnpoint.rotation);
     }
 }