Break time calculator in c#

private void button1_Click(object sender, EventArgs e)
        {
            int totalhours = 8;
            int totalmins = 0;
            int intimeHour = Convert.ToInt32(textBox1.Text);
            int intimemins = Convert.ToInt32(textBox2.Text);

            DateTime a = new DateTime(2010, 05, 12, intimeHour, intimemins, 00);
            DateTime b = new DateTime(2010, 05, 12, totalhours, totalmins, 00);
            double balhours = Convert.ToDouble(b.Subtract(a).TotalMinutes);
            TimeSpan t = TimeSpan.FromMinutes(balhours);
            string hours = Convert.ToString(t);
            int onlyhour = Convert.ToInt32(t.Hours);
            int onlymin = Convert.ToInt32(t.Minutes);
            label2.Text = "You have to be here for more " + hours + "";
            DateTime date = DateTime.Now;
            TimeSpan time = new TimeSpan(36, onlyhour, onlymin, 0);
            DateTime OfficeExit = date.Add(time);
            //TimeSpan exit = OfficeExit.TimeOfDay;
            //TimeSpan t2 = new TimeSpan(exit.Ticks - (exit.Ticks % 600000000));
            string displayTime = OfficeExit.ToString("hh:mm tt");
            label3.Text = "You have to Leave office at :" + displayTime + "";
        }