Hello @zandonella ,
To start, welcome to the HiveMQ Community! We are always happy to see new faces interested in MQTT.
This question is dependent on the version of HiveMQ that you are currently utilizing. For self-managed brokers, these certificates are generated by the user implementing TLS/SSL, and as a result the duration of the certificate will be determined during the certificate chain creation process.
For HiveMQ Cloud brokers, the current certificate is always available from the ‘FAQ’ section of our community forum (here), or via direct link (here). This currently has an expiration of June 4th, 2035.
Additionally, Cloud users utilizing Starter, Professional, or Enterprise tiers are able to provide their own certificates as well, similarly to self-hosted users, which allows for users to provide their own certificates, and as a result dictate their own expiration periods. A blog post regarding this feature is available here.
Best,
Aaron from the HiveMQ Team