If I say 1 hour, I mean that I know exactly which knob needs to be twiddled, perhaps because I wrote it in the first place, and that there'll be a pull request ready for review an hour from now.
That's clearly not always possible. Sometimes it is. If I say that it is, then I can deliver it.
> Sometimes it is.
What's the worst case of the other times? These "one hour" estimates are the golden path, nothing goes wrong, minimum. It's not the average of horror shows or an amortisation all the related support work required to sustain efficient development over time. They are often too coding-focused and ignore the level of interpersonal work to agree and sign off features or to change code in collaboration with others. Talking through a demo can take more time than the code.