how fast is this perception speed?

[Shiraito983]

It felt as if the world around him was flowing in slow motion.

Fluttering leaves seemed to freeze, and he could discern each individual grain of sand swirling in the air.

 

[Suigetsuhyugs]

It felt as if the world around him was flowing in slow motion.

Fluttering leaves seemed to freeze, and he could discern each individual grain of sand swirling in the air.

Sorry but it's not much to go on, that just points out to significantly faster than wind which is not much wind is normally pretty slow

 

[DivineAura44]

It felt as if the world around him was flowing in slow motion.

Fluttering leaves seemed to freeze, and he could discern each individual grain of sand swirling in the air.

The first part "Fluttering leaves seemed to freeze" is too vague to go off of.
The second part "he could discern each individual grain of sand swirling in the air" lacks context as well. How many grains of sand are there? How long is said sand swirling in the wind? Is he an average counter? Some characters have good counting ability allowing them to do this with normal reaction time but if not stated otherwise, we could assume he's average.
It all sounds impressive, and definitely not something a human could do but doesn't have enough to determine an exact speed from my perspective.

 

[Arkenis]

This is probably just perception manip. Seeing each grain of sand in the air is enhanced senses for one, and perceiving a leaf frozen, I think could be calc but some stuff is unknown like how far the viewer is from it and how far the leaf is from the ground, etc.