They are exactly the same as the 100th or 100,00th time---one in five for the entire cycle, one in four if the sex occurs near ovulation.
Try this little experiment. Take five identical straws, mark one of them in some way, give them to a friend to hold, and try drawing straws for fifteen minutes. See if you're "dead excited" every time you draw the bad straw. Realize that you're just as likely to draw the bad straw on your first try as your last.