This is a Bridge-to-Gantry time. In other words, not a full lap.
Many timed 'Ring “laps” are measured from the entry on to the track to the exit – this is a “bridge to gantry” lap (BTG) and misses out the part between the last gantry and the first bridge. A full lap is 20.832km, and a BTG lap is 19.1km, which equates to around 20-30 seconds less time.