The OpenCms 5 series used a version of the cron expression that is rooted in the traditional UNIX
cron server. In this format, there are only five fields (minute, hour, day, month, and day-of-week).
But OpenCms 6 has an extended cron expression format that is much more suitable for an enterprise environment. It has seven possible fields (with seconds and years added to the original five) and some convenient synonyms (such as month and day names that can be substituted for numbers in the appropriate fields).
Unfortunately, the changes are such that cron expressions that worked in OpenCms 5 will definitely not work in OpenCms 6.