Time fields
date_posted: when the source says the posting was published. It can be older thandate_created(a posting we found days after it went up). Use it for "posted this week" filters (date_posted_gte).date_created: when this index first saw the posting. Always set and only increasing: use it for incremental syncs (date_created_gte).date_last_seen: the last time the source still listed it.date_modified: when a tracked field changed upstream (modified-jobs). Re-reading an unchanged posting never sets it.date_valid_through: the closing date, when the source states one.
All times are UTC. Postings are served with no delay after indexing.