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;
     }
 }