Hi @MJohnson068,
Going forward, you would set up a deal based workflow that enrolls records when the amount property is known, then sets the close date to the date when the action is executed. Only enroll records that meet the criteria after turning the workflow on, or else all records get today’s date as close date.
This only works going forward and there is no way to access the date when a property was changed or filled within a workflow. This simply can currently not be done.
If you still want to backfill the close date according to that logic, you would have to export the property history of your amount property: Export property history
This file will include the date when the amount was populated and the deal ID. After cleaning up the file, you can reimport it into HubSpot, mapping the deal ID and the date column to the close date.
This is the only way to access this information without the help of a developer and the HubSpot API.
Let me know if you have any follow-up questions!