The assumption is that it's already unreasonable to expect developers to estimate how many hours something will take, and then due to meetings and such it's effectively impossible for them to then those already bad numbers into calendar days. So instead, the proper answer is to bypass all that by having developers estimate in made-up units that can be added up and trivially converted into calendar days.
The assumption that anyone can estimate work they have never done with a reasonable degree of accuracy is just plain wrong. That is why management pretends they arent doing that either
