You're simply playing standby roulette. If there is a flight at 7PM (or later) they will put you on it. If not, you might not get out until the next day. Technically you cannot change routing on either standby or same-day confirmed, and without knowing where you're going it's not possible to say if there would even be a connection that late in the day, but the odds aren't good. At some point if there is no nonstop the GA may take pity and put you on a connection, but there's no guarantee if or when this will happen.