In Asp.Net Forms Authentication, how can you specify the timeout property programmatically ?

HttpCookie cookie  = FormsAuthentication.GetAuthCookie (txtUserName.Text, true);

' Expires in 30 days, 10 hours and 00 minutes from today.

cookie.Expires = DateTime.Now.Add(New TimeSpan(30, 10, 20, 0));

Response.Cookies.Add (cookie);

Response.Redirect (FormsAuthentication.GetRedirectUrl (txtUserName.Text, true));