Your reservation is a two-hour block (exact wording taken from the planning site) and if they did still allow people in past a certain lateness, they'd therefore risk running into the next ceremony (also a problem with real life ceremonies that start late!).

Yes this isn't real life, it COULD have been instanced, but for whatever reason they chose not to do that with Eternal Bondings. Sorry, harsh as I know this'll sound, but they gave you a reservation for 11am (the time you picked), you weren't there, not really their fault if it didn't go ahead.