About "In the blink of an eye"

[TheGunsFinalWrath]

"In the blink of an eye" So, I've encountered words like this several times, across different novels and such, but, I dont understand what it means, as in, how much? How many seconds, or how quick did things apparently happen in this period of time? Let me show an example of how one like this looks like:

In the sealed space of the underground parking lot, the muffled sounds of fists and feet colliding could be heard. Chu Nan and Luo Jie exchanged blows, >>and in the blink of an eye,<< they had exchanged more than a hundred moves.

(I mainly encounter sentences like these in chinese novel ig.) So, any idea, anybody? How many seconds is it?

 

[GoldExPoints]

In the blink of an eye means within the duration it takes for our eyes to have one natural, instinctual blink. Said duration varies among humans the same way heartbeats do, but a common benchmark/baseline is 100 milliseconds or 0.1 seconds. So assuming "a move" is just a punch, and their arm length is 75 cm.

75 x 2 (since they need to pull back every time as well)
150 x 100 (repeat it at least a hundred times)
15000 / 0.1 (Distance / Time)
150000 cm/s = 1500 m/s = Supersonic+

And that's only accounting for punches, they kicked too.