It's the minimum length of time a video must be in order to enable mid-roll ads.
The 10 minutes one seems pretty arbitrary, but to arrive at 8 mins I suspect that Google studies how much time there needs to be so that mid-roll ads don't negatively affect engagement.
(Shout-out to all the wonderful, brilliant engineers working on figuring out how to minimize the user's reaction to cramming AS MANY ADS as possible down their brain)
extremely recently, like a week ago or so, and this video was from 3 days ago; for the next few weeks I'm still going to look at the 10 min timestamp as more telling than an 8 min one (though I'm sure youtubers will "migrate").
Looking at the channel, 3 of its videos are between 10:04 and 10:09 long. Of course, that's nothing compared to a lot of other long-form youtubers I've seen with like 80% of their videos around that timestamp.
