Convert a numeric field into an actual date:
DATEPARSE(“yyyyMMdd”, STR([Date]))

Counting Days within a Dynamic Data Set:
MAX(DATETRUNC('day',[Date Time]))-MIN(DATETRUNC('day',[Date Time])) + 1

Subtract hours from date:
DateAdd('hour', -4, [DATE FIELD])

Combine date and time from two different fields:
DATEADD(
	'hour', DATEPART('hour', [Order Time]), 
	DATEADD(
	'minute', DATEPART('minute', [Order Time]), 
	[Order Date]
	)
)