We didn't do RSVP last year, but did it the year before. We were on the second bus to depart Vancouver and didn't get back to Seattle until 4pm. The border crossing was painfully slow. To be safe, I would go with later flight if possible. Even if you get back in time, your bikes may not make it in time. We live 15 miles from start and I think we came back later to get our bikes because they weren't back yet.

It's a great ride! Enjoy!