The Sandbox Refresh Calculator (https://sandbox-preview.herokuapp.com/) simplifies how customers can plan their refreshes around our Major Releases 3x/year.

The key steps that need to be performed:

1. Review your org to identify all the critical sandboxes that need to be considered during a particular release window.

2. Use the Sandbox Refresh Calculator to quickly determine if a Sandbox instance is currently a Preview or Non-Preview sandbox.

3. Figure out if/by when you may need to trigger a Sandbox Refresh to achieve your business goals.

If folks want/need to refresh their full copy sandboxes, be sure to plan ahead. That way you can be confident that the refresh is completed in time for a given release date.