That scheduling thing is very difficult. Sylvia's already pointed out the fact that US and Canadian Thanksgivings fall at slightly different times.
I'm in the UK, and though we have a Northern Hemisphere calendar for the school year, it's not quite the same as the US one.
I see people in May talking about the "end" of the school year, where we have a few weeks to go. Equally, (I'm talking University year, rather than what I call "school"!), you're talking about going back at the end of August; we go back early October.
And, right now, the Antipodean Christmas is about to start...
I guess that it's going to be almost impossible to have a 3 week block in which it's not a busy time of year for one group.
Sylvia's already said that if there's a follow up to this, it won't be at the same time next year; which is, I think, the only thing that can really be done. Next time, the US group will have fewer other commitments, but some of the rest of us may. (Unless she locates this mythical 3 week block!)