I don't think they have a rigid system, but this post indicates that they try to...

raziel2p on Aug 9, 2020 | parent | context | favorite | on: Linux 5.8-rc1

I don't think they have a rigid system, but this post indicates that they try to make it the last release of the year: https://people.kernel.org/gregkh/next-long-term-supported-ke...