Hello, how do I display in text the amount of time before the cool down ends in this script?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class AttackCoolDown : MonoBehaviour
{

public float cooldownTime = 5;

private float nextFireTime = 0;

private void Update()
{
    if(Time.time > nextFireTime)
    {
        if(Input.GetKeyDown(KeyCode.E))
        {
            Debug.Log("Cooldown has started.");
            nextFireTime = Time.time + cooldownTime;
        }
    }
}

}

public UnityEngine.UI.Text cooldownText; // Drag & drop UI text in inspector

 private void Update()
 {
     if(Time.time > nextFireTime)
     {
         cooldownText.SetActive(false);
         if(Input.GetKeyDown(KeyCode.E))
         {
             Debug.Log("Cooldown has started.");
             nextFireTime = Time.time + cooldownTime;
             cooldownText.SetActive(true);
         }
     }
     else
     {
         cooldownText.text = (nextFireTime - Time.time).ToString("F0");
     }
 }