How to do slowly rising bar?

Hi all. I’ve got a problem with rising lvl bar. My bar doesn’t rise slowly. It appears realy fast or it rise but to fast to it’s impossible to see it. What I have to do to make it rise slowly?
I tried Time.deltaTime and Time.scaleTime and use void Update instead of void Start but it didn’t work.

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

public class fiolkaScript : MonoBehaviour {

	public Image flk;  
	float flkshow;

	void Update () {

		Time.timeScale = 0.2f;

		if(PlayerPrefs.HasKey("currentScore")){
			flkshow = PlayerPrefs.GetInt("currentScore");
		}
		Invoke("flkRise",0);
	}

	void flkRise(){
		flk.fillAmount = flkshow /100;
	}
}

You could use InvokeRepeating