loop time

You can use the Pending() method to check whether there are any pending connection requests and thereby avoid blocking. You also need a timer to check whether the 5 seconds maximum wait has elapsed:

TcpClient client = null;
Console.Write("Waiting for a connection... ");
DateTime start = DateTime.Now;
while (true)
{
   if (server.Pending())
   {
      client = server.AcceptTcpClient();
      Console.WriteLine("Connected!");
      break;
   }
   else  if ((DateTime.Now - start).TotalSeconds >= 5.0)
   {
        Console.WriteLine("Timed out after 5 seconds");
        break;
   }
}