Yeah, again, just glancing at the sunclock
http://www.worldtimezone.com/datetime.html, it seems clear that there is no better solution than a set of three times, for which each region ideally participates twice.
If we did these sets of three per weekend, and left out the Wednesday time (as that will be difficult for many of us as it is the middle of the week), we might have an ideal solution, until such a time hopefully arrives when we build up enough numbers to do the "wave" across all the time zones.
So roughly speaking, it could go:
Saturday evening : Americas + Sunday morning: Oceania
Sunday evening: Oceania + Sunday morning: Europe
Sunday evening: Europe + Sunday morning: Americas
I can work out the exact details, but as far as I know, this is the only way to avoid it being the middle of the night for anyone, make sure it's the weekend for everyone, and to combine the maximum amount of people into each session.