You can apply javascript preprocessing and run it as needed with discarding anything but when you run on last day of the month:

var today = new Date();
var lastDay = new Date(today.getFullYear(), today.getMonth() + 1, 0).getDate();
return today.getDate() === lastDay ? value : -1; 

If you have numeric values, now as next step discard data if <0

If it's text data, do some other evaluation. In any case, you have criteria to discard data on all other dates but last day of the month.

This work arround can be used but you don't avoid the colection of the data, and the colection may need a bunch of resources (executing scripts, certaiin rights etc)

As far as I know yoou can return null on the java script to discard the data, avoiding the second preporcessing step.

You are correct on both points (I was not aware of null part, now I am - thanks).

For lightweight data collection items (or those that you run say once a day) it would be good enough workaround I suppose. Otherwise maybe implement this date logic already in script (or make some wrapper script) and discard when not valid.

However, I support this feature request