Great plugin, but would advise updating and allowing users to define a custom time format (i.e DD.MM.YYYY) and their own GMT.
As currently in the ChatListener class you've set it to follow "Asia/Riyadh" zone id and the ISO at the end of the string looks really bad because you formatted it with "DateTimeFormatter.ISO_LOCAL_DATE_TIME" which is a classical mistake, as you can't predefine a custom format on the SQL rows with the way you've set the website PHP code up and I cba to hardcode it into mine, so please consider updating and adding said values to the config file. Otherwise great plugin.