If you want to use $TIMESTAMP$ or a formula of that to use as part of query to fetch/update data you can do the following supported method.
Use a Get System Info step first to get the actual/current TimeStamp.
Then, run the date here through Select Values to format the date in the way we want it:
yyyyMMdd is the format that ARS will accept here.
Then you can use this TIMESTAMP in your query, for example in CMDBInput here: