A new maintenance release of the Platform occurs roughly every 6 to 8 weeks. There will, however, be occasions when a new release occurs more quickly than this; to address a security vulnerability, for example. This schedule will also slow down as a branch ages and has been superceded.
In addition to the general maintenance cycle described above, a maintenance release of the Platform will often be triggered by a maintenance release of Spring Boot. Furthermore, a new maintenance release of Spring Framework will often trigger a maintenance release of Spring Boot.
A key goal of the Platform is to provide its users with a stable set of versions that maintain backwards compatibility while also being as up-to-date as possible. To allow us to strike this balance there may be occasions when a bug in Spring Framework or Spring Boot causes the Platform to skip a version and wait for a release which resolves the issue.