Logstash Events Stats API

What do the fields duration_in_millis and queue_push_duration_in_millis in Logstash's Events Stats API response in the link below mean?

https://www.elastic.co/guide/en/logstash/current/node-stats-api.html#event-stats

And related to the question above - for what duration are the fields in and out aggregated for by default - last 1 hour, last 24 hours, last 7 days ? and can that default be altered?