我将如何创建交货日期通知程序

我想在确切的交货日期前 30 天通知，但我不知道该怎么做。我正在使用datagridview来显示数据库中的数据。

我想创建一个倒计时，每天通知我，直到确切的交货日期。

DateTime answer = today.AddDays(30);`enter code here`
string convert1 = today.ToString("MM/dd/yy"); //Today's date
string convert = answer.ToString("MM/dd/yy"); //Today + 30days
sqlcon.Open();
command.Connection = sqlcon;
command.CommandText = "SELECT [ID], [Delivery Date], [Delivery Time], [Delivery Description] From Delivery WHERE [Delivery Date] < '" + convert + "' ORDER BY [Delivery Date] ASC";
using (SqlDataReader reader = command.ExecuteReader())
{
    while (reader.Read())
    {
        if (today.Date < answer.Date)
        {
            MessageBox.Show("Upcoming Delivery in less than 30 days!" + "'n'n*Delivery Date:'n" + "     " + reader["Delivery Date"].ToString() + "'n'n*Delivery Description:'n" + "     " + reader["Delivery Description"].ToString());
         }
     }
 }
 sqlcon.Close();