When does the backlog snapshot happen in Zendesk Explore?
Explore collects backlog information every time your data synchronizes with Explore. If you are on the Explore Lite plan, data synchronizes once every 24 hours. If you are on the Explore Professional or Enterprise or Legacy plan, data synchronizes one hour after the most recent sync ended.
To see your current backlog, create an Explore query based on the metric # Tickets from the Backlog history dataset at any given date in the past other than today.
For more details about the backlog, see the article: Backlog history dataset.