I'm flying from IND to BRU via IAD next week, and am booked on a 6am departure from IND connecting to a 543pm departure from IAD to BRU. Don't ask -- when I bought the ticket it priced out at $500 less than the optimal connection, which leaves IND at 230pm. I asked reservations if I could standby for the later flight and the agent said I could, of course recommending that I check loads the night before. I asked her if my continuing reservation would be cancelled and she said it would not because it usually "takes 24 hours to clear the system." Does anyone have any experience with this type of scenario? If I show up within two hours of the original flight, will they rebook me on the later flight?

(Oh, well, I guess I should just get up early and arrange some meetings in DC.)