Pre-game vs in-play lines
Pre-game lines are set before the event and move slowly; in-play lines reprice every few seconds during it.
In-play quotes go stale so fast that a scan a minute old is meaningless, and a book's displayed in-play price is often unavailable by the time a bet is placed. ArbMonster scans pre-game lines only and refreshes them every 15 minutes; in-play scanning is on the roadmap with tighter freshness guarantees.