Hi @David ,
Yes, that is correct. This is confirmed in this Azure doc:
"The free App Service managed certificate is a turn-key solution for securing your custom DNS name in App Service. It's a TLS/SSL server certificate that's fully managed by App Service and renewed continuously and automatically in six-month increments, 45 days before expiration, as long as the prerequisites set-up remain the same without any action required from you. All the associated bindings will be updated with the renewed certificate. You create the certificate and bind it to a custom domain, and let App Service do the rest."
Hope that helps.
Best,
Grace