Как сделать таймер в Windows Forms?

using System;
using System.Windows.Forms;
 
namespace TempWinFormProject {
    public partial class Parent : Form {
        public Parent() {
            InitializeComponent();
 
            tm = new Timer();
            tm.Tick += new EventHandler(tm_Tick);
            tm.Interval = 1000;
        }
 
        Timer tm = null;
        int startValue = 0;
 
        private string Int2StringTime(int time) {
            int hours = (time - (time % (60 * 60))) / (60 * 60);
            int minutes = (time - time % 60) / 60 - hours * 60;
            int seconds = time - hours * 60 * 60 - minutes * 60;
            return String.Format("{0:00}:{1:00}:{2:00}", hours, minutes, seconds);
        }
 
        void tm_Tick(object sender, EventArgs e) {
            if(startValue != 0) {
                label1.Text = Int2StringTime(startValue);
                startValue--;
            } else {
                (sender as Timer).Stop();
                (sender as Timer).Dispose();
                MessageBox.Show("BadaBoom!");
            }
        }
 
        private void buttonStart_Click(object sender, EventArgs e) {
            startValue = 60 * 60 * (int)numericUpDownHour.Value + 60 * (int)numericUpDownMin.Value + (int)numericUpDownSec.Value;
            tm.Start();
        }
    }
}