When does the backlog snapshot happen? Is it at 00:00? At the end of the working day?
The backlog is recorded on an hourly basis when your Zendesk data syncs with Explore (see How frequently does my Zendesk data sync to Explore?).
To see your current backlog, create an Explore query based on the metric # Tickets from the Support Ticket Backlog dataset at any given point of the day. You don't need to wait until the end of the day to see today's backlog.
For more details on which metrics and attributes you can use to report in Explore, see Backlog History dataset.