unity - Why the timer is not showing the hours?

It's showing minutes seconds milliseconds but I want to show also the hours.

At the top:

private int seconds; // Seconds.

private int minutes; // Minutes.
private int hours;   // Hours.

In Update:

void Update()
{
if (seconds < 1)
        {
            seconds = 59;
            minutes--;

        }
        if (minutes < 1)
        {
            minutes = 59;
            hours--;
        }
        if (hours < 1)
        {
            hours = 59;
        }

        seconds--;

        EditorGUILayout.LabelField("Next: ", hours.ToString() + ":" + minutes.ToString() + ":" + seconds.ToString());

Update, This is what I tried:

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEditor.SceneManagement;

using UnityEngine;
using UnityEngine.SceneManagement;

public class Timer : EditorWindow
{

    private static Timer editor;
    private static int width = 300;
    private static int height = 110;
    private static int x = 0;

    private static int y = 0;
    int totalSeconds;

    [MenuItem("Window/Timer")]
    static void ShowEditor()
    {
        editor = EditorWindow.GetWindow();
        editor.Init();
    }


    public void Init()
    {
        StartTimer(1, 1, 50);
        Debug.Log("The level will now be saved automatically");
    }

    void OnGUI()
    {
        EditorGUILayout.LabelField("Next: ", TimeString());
    }


    public void StartTimer(int hours, int minutes, int seconds)
    {
        totalSeconds = seconds + 60 * minutes + 60 * 60 * hours;
    }

    string TimeString()
    {
        return string.Format("{0:00}:{1:00}:{2:00}",
                      totalSeconds / (60 * 60),   // Hours

                      (totalSeconds / 60) % 60, // Minutes
                      totalSeconds % 60);     // Seconds
    }
}

But the timer is not moving not counting back it stay still. I tried also to move the line:

StartTimer(1, 1, 50);

To be inside the OnGUI before the LabelField.

Answer

Writing your own date and time handling code from scratch is a path towards agony and despair. It is usually far better to use the time handling features provided by your platform. In the case of C#, the standard library offers you a handy TimeSpan class.

 TimeSpan timer = new TimeSpan(1, 1, 50);
 Debug.Log("The timer is set to " + timer.ToString("hh\\:mm\\:ss"));

The class also has a bunch of methods which allow you to modify the value in an easy and painless way. For example, if you want the Update method of a MonoBehaviour to reduce the remaining time:

 Update() {
    TimeSpan deltaTimeSpan = TimeSpan.FromSeconds(Time.deltaTime);
    timer = timer.Subtract(deltaTimeSpan);
    Debug.Log("Time left: " + timer.ToString("hh\\:mm\\:ss"));
 }