How to I start my jump boost power up timer when player collides with power up?

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class JumpPowerUp : MonoBehaviour {

	public GameObject PowerUp;
	public GameObject RunningMan;
	private float timer = 0;
	float jumper;



	void OnTriggerEnter2D(){
		RunningMan.GetComponent<RunningManMov> ().jump = 9;
		Destroy(PowerUp);
	}

	void OnTriggerExit2D(){
		timer += 1
	}

	void Update(){

		jumper = RunningMan.GetComponent<RunningManMov> ().jump;

		if (timer > 5) {
			RunningMan.GetComponent<RunningManMov> ().jump = 6;
		}
	}

}

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class JumpPowerUp : MonoBehaviour {

	public GameObject PowerUp;
	public GameObject RunningMan;
	private float timeExited = 0;
	private float timeForPowerUpToLast = 5;
	float jumper;



	void OnTriggerEnter2D(){
		RunningMan.GetComponent<RunningManMov> ().jump = 9;
		Destroy(PowerUp);
	}

	void OnTriggerExit2D(){

		// Get access to the current time
		timeExited = Time.time;
	}

	void Update(){

		jumper = RunningMan.GetComponent<RunningManMov> ().jump;

		// A timer that lasts for five seconds
		// Current time subtracted by the time you exited the trigger
		if (Mathf.Abs (Time.time - timeExited) >= timeForPowerUpToLast) {
			RunningMan.GetComponent<RunningManMov> ().jump = 6;
		}
	}

}