[Data Integration] How can I generate and include a timestamp on a Data Export to File extract?

I am looking to add a timestamp on a data extract via the Data Export to File target application type. From what I can tell, this is not a straightforward task, but I could be missing something.

My current idea is to use Groovy to dynamically populate a timestamp as a constant in the Source Expression for extract date field. However, I'm having trouble finding exactly how to update that via Groovy prior to the extract running. Can anyone point me to the Oracle documentation on the proper naming/convention to update this (I can't seem to find it).

If anyone has any information or other suggestions outside of the Groovy approach (SQL in Source Expression?), I would really appreciate it. Thanks!