DJI has unveiled its latest gimbal, the Osmo Mobile 5. The OM 5 is much lighter than its predecessor but with a built-in extension road, 3-axis stabilisation and ActiveTrack 4.0. There is one major disadvantage with the OM 5 compared to the OM 4, though.
https://www.notebookcheck.net/DJI-Osmo-Mobile-5-introduced-with-3-axis-stabilisation-ActiveTrack-4-0-and-a-much-lighter-chassis.559563.0.html
6 hours 24 minutes is written as 6.4 hours because 24 hours is 0.4 fraction of one hour.
24 minutes out of 1 hour = 24 minutes out of 60 minutes = 24 parts out of 60 parts = 4 parts out of 10 = 4/10 (read 4 by 10 or 4 upon 10) in fraction or 0.4 in decimals.
so, 6 hours + 24 minutes = 6 hours + 0.4 hours = 6.4 hours.
It's not a typo.