instantiating at a random time

Questions & Answers
1

trying to instantiate a prefab at a random time.Do I use coroutine to stop the instantiated object for a few seconds or is there any other way?I would be very grateful if someone could edit my code because I am a new unity/C# user.Thanks

using UnityEngine;
using System.Collections;

public class aeroplane_prefab : MonoBehaviour {
    //private GameObject aeroplane_prefab;
    // Use this for initialization
    void Start () {

        setInitialPosition();

    }
    // Update is called once per frame
    void Update () {

        float speed =Random.Range(20f,10f);
        transform.Translate(Vector3.back * speed * Time.deltaTime);

        if (gameObject.transform.position.z <= -38)
        {
           //Destroy(gameObject);
          // 
            StartCoroutine(enemySpawn());
            Instantiate(gameObject, transform.position, Quaternion.identity);
        }
    }

    void setInitialPosition(){
        float randomy = Random.Range(36f, 46f);
        float x = 0;
        float y =randomy;
        float z = 45f;
        transform.position = new Vector3(x, y, z);
    }

    IEnumerator enemySpawn()
    {
            //Destroy(gameObject);
            yield return new WaitForSeconds(10f);
            Debug.Log("timeup");//just to check if its working

            }
 }
2

e.g. instantiate code with a yeild

var prefab : GameObject;

function Start(){
   var waitTime : float = Random.Range(0.0,100.0);

   yield WaitForSeconds(waitTime);

   Instantiate(prefab);
}

http://unity3d.com/support/documentation/ScriptReference/WaitForSeconds.html