This returns whether or not the given Date and Time is a work day, according to the calendar defined for the system.
calisworkday( datetime, [calendar name] )
datetime: (Date and Time) The Date and Time to test.
calendar_name: (Text) This optional parameter accepts the name of a system calendar; otherwise, the default calendar is used.
Boolean
Passing a calendar name allows you to validate working days using an alternate system calendar, if you have multiple calendars configured.
See also: Process Calendar Settings
calisworkday(datetime(2011,12,13,20,0,0),"Second")
returns true