Update: The FreeSewing contributor call is scheduled for Saturday, September 5, 2020 at 16:00 UTC. Which is:
Los Angeles: 09:00 Chicago: 11:00 New York: 12:00 São Paulo: 13:00 London: 17:00 Paris: 18:00 Johannesburg: 18:00 Moscow: 19:00 Mumbai: 21:30 Hong Kong: 00:00 on Sunday, September 6, 2020 Tokyo: 01:00 on Sunday, September 6, 2020 Sydney: 02:00 on Sunday, September 6, 2020
It was tied for most votes with the same hour on Sunday, but I figured that perhaps people were willing to stay up a bit later on a Saturday than on a Sunday - Or wake up a bit earlier on a Saturday than on a Sunday :)
To be clear: There was no time slot that fitted everyone. This was the one that worked for most people.