@Luigi259 Yes, that's right. I have two properties! I didn't know that this affects the options.
Did you try to open the calendar and set the rules there? If you chose one or more days like a whole period, in the context menu on the right side, section rules, there might be an option to set check in or check out days. Does this work? If yes, make sure to click "confirm" in the context menu to keep settings and not just leaving the calendar, because otherwise the rules would not apply.
Don't know if it is available for everyone or just hosts with two properties.