To make it even worse, these "awake zones" will start spanning multiple weekdays. So, when is Sunday, again? Is that the period of daylight that starts at 21:00

To make it even worse, these "awake zones" will start spanning multiple weekdays. So, when is Sunday, again? Is that the period of daylight that starts at 21:00 on Saturday and lasts until 09:00 Sunday? Or is it the period that starts at 21:00 on Sunday and lasts until 09:00 Monday? When's your business open, again? Timezones are extremely useful.