"exactly 24 hours" could still be anywhere between 86399 and 86401 seconds, depending on leap seconds. At least if by an hour you mean an interval of 60 minutes, because a minute that contains a leap second will have either 59 or 61 seconds.

You could specify that for the purposes of cooldowns you want "hour" to mean an interval of 3600 seconds. But that you have to specify that should illustrate how ambiguous the concept of an hour is. It's not a useless concept by any means and I far prefer to specify duration in hours and days, but you have to spend a sentence or two on defining which definition of hours and days you are using. Or you don't and just hope nobody cares enough about the exact cooldown duration