How to send mail after a particular peroid

protected void btnSubmit_Click(object sender, EventArgs e)
{
try
{
MailAddress SendFrom = new MailAddress(txtFrom.Text);
MailAddress SendTo = new MailAddress(txtTo.Text);

MailMessage MyMessage = new MailMessage(SendFrom, SendTo);

MyMessage.Subject = txtSubject.Text;
MyMessage.Body = txtBody.Text;

Attachment attachFile = new Attachment(txtAttachmentPath.Text);
MyMessage.Attachments.Add(attachFile);

SmtpClient emailClient = new SmtpClient(txtSMTPServer.Text);
emailClient.Send(MyMessage);

litStatus.Text = "Message Sent";
}
catch (Exception ex)
{
litStatus.Text=ex.ToString();
}
}