The FAs have NO clue what altitude the airplane is flying at. On flights with the airshow, I'm pretty sure they're not going to look at that to determine when to make their announcements. If you've noticed, they take cues from the chiming system set in place from the flight deck. We have our flows and procedures which involve chiming the FAs at pre determined times. When they hear their chime, they make their announcements. And this, one more time, is a function of the manuals and procedures the FAA have approved for all 9 carriers. DL has, from what I can tell, attempted to align the DCI announcements to their own. Chiming, etc... may be different.

The time between passing 10,000 and landing does not come with a pre set timeframe. It can happen quick, can happen slow or can easily turn from what we THOUGHT was going to be quick, into something slow or vice versa. So, it may seem like the FAs are doing their jobs early, but it just might be a matter of passing through 10,000 feet and "lingering" so to speak, which makes the passenger feel like they've been duped into a conspiracy that the FAs have stirred up to get electronic devices turned off early.