Should we add another utc_index or localtime parameter and add the following logic here: 
if @utc_index
  target_index = "#{@logstash_prefix}-#{Time.at(time).getutc.strftime("#{@logstash_dateformat}")}"
else
    target_index = "#{@logstash_prefix}-#{Time.at(time).strftime("#{@logstash_dateformat}")}"
end