As for the "hours" max interval, this is the result of a design decision in Go's time duration library, dealing with the quirks of our calendaring system.
It's because units up to hours are of a fixed size, but days in most places are only 24h for ~363/365 days of the year, with some being 23h and some being 25h.
(This is ignoring leap seconds, since the trend is to smear those rather than surface them to userspace.)
As for the "hours" max interval, this is the result of a design decision in Go's time duration library, dealing with the quirks of our calendaring system.