You can send commands and read responses on your own. The following sample code solves your needs:
Pop3 client = new Pop3();
client.Connect("pop.gmail.com", 995, null, Pop3Security.Implicit);
int delay = -1;
client.SendCommand("CAPA", true);
for (string response = client.ReadResponse(); response != null; response = client.ReadResponse())
{
if (response.StartsWith("LOGIN-DELAY", StringComparison.OrdinalIgnoreCase))
delay = int.Parse(response.Substring(12).Trim());
}
Console.WriteLine(delay);