Instance of a calendar that performs date based operations like adding or calculating differences by rules.

Default calendar instance exposed as $Calendar variable that executed by domain rules. Default domain rules are includes Monday to Friday and 9:00 AM - 18:00 PM hours. All date calculations performed within this included time range.

Also you can use Calendar.GetStandardCalendar to use a calendar with no rules or Calendar.GetWeekendCalendar to include only Monday to Friday days without no hour limitation.