Tim Cook
Apple CEO Tim Cook included an interesting, hidden tid-bit in his commemorative tweet for the iPhone's 10th anniversary.Robert Galbraith/REUTERS

Apple CEO Tim Cook took to Twitter on Thursday to commemorate the iPhone's 10th anniversary. However, many may have missed an interesting detail in the seemingly simple post that featured a photo of the original iPhone.

"Here's to the #iPhone that changed the world, to the man who dreamed it, and the people at Apple who have never stopped looking to its future," Cook tweeted.

Some eagle-eyed Apple fans, however, spotted that the tweet was sent out at exactly 9:41AM. In fact, the clock on the image of the iPhone also reads the same, as it does across much of Apple's product advertisements on its site and elsewhere.

When the late Apple co-founder Steve Jobs unveiled the very first iPhone, his keynote at Macworld Conference & Expo in San Francisco began at 9AM. However, he only officially announced the device at 9:42AM.

"Today Apple is going to reinvent the phone", Jobs said onstage before the screen behind him displayed a picture of the first iPhone.

The iPhones seen in earlier Apple ads were also shown featuring the same time.

"We design the product launch keynotes so that the big reveal of the product happens around 40 minutes into the presentation," former Apple executive Scott Forstall told The Atlantic in 2014. "When the big image of the product appears on screen, we want the time shown to be close to the actual time on the audience's watches. But we know we won't hit 40 minutes exactly.

"And for the iPhone, we made it 42 minutes. It turned out we were pretty accurate with that estimate, so for the iPad, we made it 41 minutes. And there you are—the secret of the magic time."

In recent years, Apple slightly tweaked it to have the time 9:41AM featured in its promotional materials.