I did it! Script to compute UNIX time!

:local A [$datetime2epoch “2023-09-30 16:55”]
1696085700

:local B [$datetime2epoch “2023-08-31 16:55”]
1693493700

Result:
A - B / 86400 = 30 days
Note: The converter to change the Changelog date to the MT date can be found at:
http://forum.mikrotik.com/t/script-to-update-routeros-after-x-days-of-release/170000/1

Good luck!