Maybe some more information (and an example) would help.
In its most basic, something like this...
IF MAX([Date 1]) > MAX([Date 2]) THEN MAX([Date 1]) ELSE MAX([Date 2]) END
If Date 1 is greater than Date 2, return date 1
otherwise (date 1 is not greater than date 2) so return date 2 (its therefore the larger)
You could use WINDOW_MAX, it depends on your data and setup.
You're very welcome, does that answer your question?