Last summer, coming back from Canada, my husband was going to have to have an overnight connection at DFW. After he had purchased the ticket, but before the flight, another flight was added that, if he could get on it, would get him back to TUL that night. As soon as he arrived at DFW, he ran over to the gate for the TUL flight and asked to standby. They said no problem. He got on the flight. Thank Heavens, because the next morning was when the infamous gel and liquid restrictions were instituted with no advance warning.

I think the rule about not standing by for a flight the day prior to your ticketed flight does not apply if there is an overnight connection.