Just to elaborate a little, the local timezone is set in three different places: OS, Java, openHAB. Java is supposed to inherit from the OS but for reasons no one has been able to figure out it does not always do so.
If cron doesn’t fire at the correct times or if you notice the timestamps in your logs being off that’s often an indicate that that the Java timezone setting is incorrect. If the OS is set properly that means Java didn’t pick it up so you need to add the extra Java option as shown.