This nicely recapitulates phylogeny: in the origin of Babylonian timekeeping (we all now use a system based on that), hours were not of a fixed length; there were twelve of them between dawn and dusk and twelve more between dusk and dawn.
Minutes (as can be see from their clearly Latin name, "tiny") and the second division of them (seconds) are brand new and AFAIK have always been of fixed length, a consequence of mechanical timekeeping.
Minutes (as can be see from their clearly Latin name, "tiny") and the second division of them (seconds) are brand new and AFAIK have always been of fixed length, a consequence of mechanical timekeeping.