I would use your CRM if you are able to.
Another hacky option is create a "counter" using a score field, do a +1 increment daily for members of the counter program and at 30 days take your desired action then reset counter and remove individual - or whatever you see fit.
I have used this method a number of times.
This thread is from 5 years ago!
(Also, Velocity can be used to do this as described.)