This functionality is currently not available easily without a bit of "coding" (see below). But it's a nice Feature Request. I have added a FR for it: #8073
forge.joomlapolis.com/issues/8073
You can make it work now already with a little bit of SQL "coding", by using 2 CB Auto-Actions of:
- Type "Query",
- triggering on "onBeforeRegisterForm"
- with condition CB field "[cb:date format="Y-m-d" /]" "greater than or equal to" "2020-07-30" (e.g. to start on 30th of July, and obvious "smaller than" condition for the second auto-action)
- and a query (adapt) like: "UPDATE #__cbsubs_plans SET allow_registration = 1 WHERE allow_registration = 0 AND id = 1;" (for plan id 1: adapt your plan id, and obviously the reverse for disallowing registrations at end date).
That's for registrations. For upgrades, it would be "allow_upgrade_to_this".