How do i get this to spawn over time?

How do i get this script to spawn over time, so the longer you wait the more objects it spawns. how would i do this?here is my curren code.

  using UnityEngine;
  using System.Collections.Generic;

  public class PlatformManager : MonoBehaviour {

  public Transform prefab;
  public int numberOfObjects;
  public float recycleOffset;
  public Vector3 minSize, maxSize, minGap, maxGap;
  public float minY, maxY;

  private Vector3 nextPosition;
  private Queue<Transform> objectQueue;

   void Start () {
     objectQueue = new Queue<Transform>(numberOfObjects);
     for(int i = 0; i < numberOfObjects; i++){
         objectQueue.Enqueue((Transform)Instantiate(prefab));
     }
     nextPosition = transform.localPosition;
     for(int i = 0; i < numberOfObjects; i++){
         Recycle();
     }
   }
   void Update () {
      if(objectQueue.Peek() == null)
      {
      objectQueue.Dequeue();
      objectQueue.Enqueue((Transform)Instantiate(prefab));
      nextPosition = transform.localPosition;
      }
     if(objectQueue.Peek().localPosition.x + recycleOffset < Runner.distanceTraveled){
    Recycle();
    }
    }

 private void Recycle () {
     Vector3 scale = new Vector3(
         Random.Range(minSize.x, maxSize.x),
         Random.Range(minSize.y, maxSize.y),
         Random.Range(minSize.z, maxSize.z));

     Vector3 position = nextPosition;
     position.x += scale.x * 0.5f;
     position.y += scale.y * 0.5f;

     Transform o = objectQueue.Dequeue();
     o.localScale = scale;
     o.localPosition = position;
     objectQueue.Enqueue(o);

     nextPosition += new Vector3(
         Random.Range(minGap.x, maxGap.x) + scale.x,
         Random.Range(minGap.y, maxGap.y),
         Random.Range(minGap.z, maxGap.z));

     if(nextPosition.y < minY){
         nextPosition.y = minY + maxGap.y;
     }
     else if(nextPosition.y > maxY){
         nextPosition.y = maxY - maxGap.y;
     }
         }
            }