Delay in time

So hi im working on making a special box where u step on it u get a special power,the ideal is when you leave it u still maintain the special power for an amount of time(3 sec) here are my code

using UnityEngine; using System.Collections;

public class SpecialPower : MonoBehaviour {

 GameObject Player;
 public bool effect = false;
 
 public bool cooldown = false;
 void Awake()
 {
     Player = GameObject.FindGameObjectWithTag("Player");
 }
 void OnTriggerEnter2D(Collider2D other)
 {
     if (other.gameObject == Player)
     {
         
         effect = true;
        
     }
 }
 void OnTriggerStay2D(Collider2D other)
 {
     if (other.gameObject == Player)
     {
         effect = true;

     }
 }

  

 void OnTriggerExit2D(Collider2D other)
 {
     if (other.gameObject == Player  )
     {
         Invoke("DoSomeThing", 3);
     }
 }
 void DoSomeThing()
 {
         effect = false;
 }

} so thank you for reading my post and if u guy can help i will be glad