I suppose the $6m question is, how much time do we really need on Rotto? If we're happy to take the 0830 ferry from Barrack Street, do the bus tour (or similar), and return on the 1410 ferry to Freo and then train back, it would be fine doing it on Sat. Let's face it - it's a really tight day, and personally, I probably would prefer more time, but the fact remains that most of us aren't going to be interested in riding a bike around the island, or snorkeling in the bays that most likely wouldn't have had time to warm up. Those who feel that they don't need the couple of hours to refresh before the main dinner can hop over to Little Creatures in Freo, and then catch a later train back to PER and head straight for the venue.
I did mention about doing Rotto on the Sunday, but now I realised that none of the return ferries would work with the flight schedules.
PER-MEL is around 1700 for both QF and VA, and the next flights after that are redeyes.
PER-ADL is at 1710 for both QF and VA, with nothing after that. (VA has the e90)
PER-SYD is around 1500, or red eye.
PER-BNE has a QF service at 1625, and then red eyes.
*I only checked QF and VA. I can't see any of us flying on the other airlines.
Note that the 1410 ferry arrive at Freo at 1500, and you need a minimum of 90 mins to get from the ferry terminal at Freo (B-shed) to the airport. So basically, I think Rotto on Sunday simply won't work for the vast majority of attendees.