RelativeDateTime()

Function reference
Obtains a datetime that occurs a specified number of seconds after or before another datetime.

RelativeDateTime ( datetime, n )

Data type: DateTime
Returns the datetime that occurs n seconds after datetime if n is greater than 0. Returns the datetime that occurs n seconds before datetime if n is less than 0.

Example 1
This expression returns the datetime 24 hours ago. (2017-1-1 19:01:31)
RelativeDateTime( DateTime(‘2017-1-2 19:01:31’) , -86400)