As I can make a timer?

Simply use Invoke or InvokeRepeating on your behaviour.

http://unity3d.com/support/documentation/ScriptReference/MonoBehaviour.Invoke

I usually do something like this, because then I can easily pass parameters to it. You can simply invoke any function after an amount of seconds with this line:

 // Start a coroutine ExecuteIn, pass methodname, seconds to wait, and parameters in an object.
 StartCoroutine("ExecuteIn", new object[3] { "DoSomething", 0.5f, new object[2]{ "I love this", 100f}});

like in this script:

 using UnityEngine;
 using System.Collections;
 using System.Reflection;
 using System;
 
 public class example : MonoBehaviour {
 
     void Start () {    
        // Start a coroutine ExecuteIn, pass methodname, seconds to wait, and parameters in an object.
        StartCoroutine("ExecuteIn", new object[3] { "DoSomething", 0.5f, new object[2]{ "I love this", 100f}});
     }
 
     // Your function you will execute after x seconds
     void DoSomething (string s, float t) {
        // Gets current executed method information. This is just for this example.
        MethodBase methodIn = MethodBase.GetCurrentMethod();
        Debug.Log("Executed method " + methodIn.Name + " at " + Time.time); // prints ca. 0.5f
        Debug.Log(s + ": " + t + " %");
     }
 
     // Gets the method name, and calls the method after the amount of time specified.
     IEnumerator ExecuteIn(object[] myMethodInfo) {
 
        Debug.Log("Starts timer at " + Time.time + " and waits before executing method: " + myMethodInfo[0]);
        // Gets the method information from string
        MethodInfo method = this.GetType().GetMethod((string)myMethodInfo[0], BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
        // waits for x seconds
         yield return new WaitForSeconds((float)myMethodInfo[1]);
        // if method found: invoke the method
        if (method != null)
        {
            method.Invoke(this, (object[]) myMethodInfo[2]);
        } else {
          Debug.LogError("Method not found");
        }
     }
 }