c#计算两个时间差

【实例截图】

【核心代码】

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        public object Label1 { get; private set; }
        private TimeSpan T1, T2,T3;
        private void button1_Click(object sender, EventArgs e)
        {
            var value = string.Empty;
            string _strWorkingDayAM = "07:30";//工作时间上午08:30
            string _strWorkingDayPM = "19:30";
            TimeSpan dspWorkingDayAM = DateTime.Parse(_strWorkingDayAM).TimeOfDay;
            TimeSpan dspWorkingDayPM = DateTime.Parse(_strWorkingDayPM).TimeOfDay;


            T1 = DateTime.Now.TimeOfDay;

            label1.Text = T1.ToString();

        }

        private void button2_Click(object sender, EventArgs e)
        {

                T2 = DateTime.Now.TimeOfDay;

                label2.Text = DateTime.Now.TimeOfDay.ToString();

        }

        private void button3_Click(object sender, EventArgs e)
        {
            T3 = T2.Subtract(T1);

            label3.Text = T3.Hours.ToString()   ":"   T3.Minutes.ToString()   ":"   T3.Seconds.ToString() ";" T3.Milliseconds ;
        }

        private void button4_Click(object sender, EventArgs e)
        {
            if (T2 > T1)
            {
                button4.BackColor = Color.Green;
            }
            else
            {
                button4.BackColor = Color.Red ;
            }
        }
    }
}