These settings apply to the calendar format application mode. You can open this mode by clicking the button at the bottom left of the board.
This section currently has only one setting, but this section may be expanded in the future. For now, you can only select which days of the week are your days off. Honestly, this setting has almost no effect. These days will simply be highlighted in red in Calendar.

Note:
Initial settings depend on your phone's regional settings.
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