Changed Records Extract

Summary

I am working on an extract that will only extract records after a certain date. I would like to see if there its a way to dynamically calculate the check date.

Content

I am utilizing extract from a hierarchy view to try and only get the nodes that have changed after a certain date. 

Currently, I am using the formula below.  

I would like the extract date to be dynamic.  Possibly something like today()-30 days.  In the current build, I need to select the extract date at the top of the hierarchy and set it up with positional inheritance.