I want my cologne to have good longevity and sillage. Therefore, I pay attention to what people say about longevity. They sometimes mention about a strong cologne which has 24 hours of longevity and I don't know what I should understand from that.

I mean, for example;

let's say it's been 3 hours since you sprayed it on your arm and you can smell it heavily.

Then 5-6 hours: it becomes closer to skin but you can still detect it.

8 hours: you need to get really close but the smell is nice and you can say that this is your cologne.

15 hours: you must try so hard to smell it and your nose have to be touching your arm. You can smell it but there is not any evidence that it is the cologne that you sprayed 15 hours ago. There is sth that smells there.

So, does this cologne last for 15-20 hours? or Is the longevity limited to the interval that you can detect the notes easily? or Is it a part of the dry down and we should say it still didn't finish smelling?

I might not have expressed it adequately but I tried

Thanks in advance.