I'm facing a situation now: There are two batches of nodes in an ES cluster. One batch loads 'user.timezone=Asia/Bangkok' from etc/timezone at startup, while the other batch loads 'user.timezone=America/Bogota'. Even though the node physical times are kept consistent using the same NTP service, I'm not sure what actual impact the nodes with different time zones will have on the cluster. Version: 6.8.1
Data indexed in Elasticsearch will always be in UTC, it doesn't matter the timezone of the server, this will probably only impact the time in the logs generated by the server itself.
Also, you have a bigger problem, version 6.8.1 is ancient and should not be used anymore, you need to look in upgrading it.