DateTime.Constructor(secondsFrom1970 as Double, timeZone as TimeZone = Nil)
From Xojo Documentation
Creates a date using number of seconds since 1 January 1970, 00:00 GMT. Use a negative value to specify a date before 1 January 1970.
This example creates the date April 1st, 1996 in the America/Chicago time zone:
Convert a date in the local time zone to the GMT time zone: