http://postmark4sthinkf6thjvikt62jnx2j7m6baa5ikntgvrtqioohetiyd.onion/about
Assuming that you have saved the status page and you see it marked as sent, then you should recieve the postcard within 3-7 days (not including sundays). If you haven't saved the status page, your postcard may have been rejected. Additionally, sometimes it takes me a while to process the queue, I do have a full time job and shit too.