It's from this review.
https://www.0db.co.kr/REVIEW_0DB/1101022
Use Google translate and look at section
5. Group Delay
translation:
"This is a Group Delay item that should be included in the Bluetooth product measurement review.
This is the item that checks how much delay occurs in each frequency band until a signal is generated and returned to the measurement equipment. It is almost 0ms for wired products. That's why wireline products don't show measurement data, but
it's very important to see how well an important antenna design is used in a Bluetooth product and whether you've used a good Bluetooth chip.
Measured at 290 ms. There is no problem in the Android phone, and in case of the iPhone, it is not inconvenient to watch videos, but if you are sensitive, you may feel a slight lag."