Calendar Methods
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.