putting PM in a DateTime format in a winform

I have a sql statement that I am trying to put a start date and an end date into. The startdate is DateTime.Today - because that returns MM/dd/yyyy 12:00:00 AM
I need the end date to be MM/dd/yyyy 11:59:59 PM  - How is this done? When I use tt it returns AM

        private void radButton1_Click(object sender, EventArgs e)
        {

            DateTime tempend = DateTime.Today;
            string format = "MM/dd/yyy 11:59:59 tt";

            string end = tempend.ToString(format);
            DateTime start = DateTime.Today;

            string newuserid = iuserid.ToString();
            string conString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();
            string sqlstr = "delete from ARoles where useruid ='" + newuserid + "' and LastEditDate between '" + start + "' and  '" + end + "'";
            HelperClasses.SqlHelper.ExecuteNonQuery(conString, CommandType.Text, sqlstr);
            this.Close();
        }

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I would appreciate the help
Thanks R3nder