Sasha, you're right! I didn't think about the time difference. We'll double check our calendars to make sure we don't have anything pressing on the later dates, then sign up for the plane tickets.
We're already booked on a VI tour in early June, so we have our discount already. You're right again; it looks like there are still plenty of spaces available, but I need to call the office to change our dates. I would hate to lock in plane tickets and then discover there's no room on the tour. We've also already reserved a hotel for before the tour in Padua, but that shouldn't be hard to change.
Someone from RSE told me once that the status changes to "Filling Fast" when there are four or fewer slots left. So unless a family group sneaks in before we can call the office, we should be okay. I'll probably go ahead and risk it, if the status stays "Sign up now."
Thanks again.
Edit:
It also occurs to me that if I sign up for the later plane tickets today (Sunday,) I can email RSE, letting them know I'll be calling Monday morning to change my tour dates.