Following is the timezone setting documentation for Logstash Date filter.
What is meant by platform default in the description? Does it mean the timezone of the server on which the Logstash is running?
Timezone Value type is string There is no default value for this setting. Specify a time zone canonical ID to be used for date parsing. The valid IDs are listed on the (Joda.org available time zones page)[http://joda-time.sourceforge.net/timezones.html]. This is useful in case the time zone cannot be extracted from the value, and is not the platform default. If this is not specified the platform default will be used. Canonical ID is good as it takes care of daylight saving time for you. For example, America/Los_Angeles or Europe/France are valid IDs.