Hi Badger , The below seemed to work for me
ruby {
init => "require 'time'"
code => "
starttime = Time.iso8601(event.get('CREATED').to_s).to_f;
endtime = Time.iso8601(event.get('RESOLVED').to_s).to_f;
event.set('time_diff', endtime - starttime);
"
add_tag => [ "calculated_time_difference" ]
}
Thank you for your input