Donald wrote:Hours maybe something to do with lunar cycles and and equal daylight/night numbers? We know there's 12 lunar cycles per year and perhaps (not 100% sure) you can only view the moon for a max of 12 hours (at least back then without telescopes)? I guess at certain times sunlight obscures viewing and the same when the earth eclipses the sun? It's fun to speculate. Even more fun to know

Yeah, but if we look at a second purely as a unit of measure then there's no need for it to correlate with lunar cycles. It's just useful if we factor them in to units that do. But if we purely want to use an organised, mathematical approach then you would surely work to the SI unit convention of a base unit, then a kilo unit, mega unit, giga, tera etc... but ironically I feel you lose the usefulness of the units if you so rigorously apply the convention that's supposed to make them less cumbersome and more interpretable.
It always just comes back to what the users of the units find most appropriate for their needs really, which to tie back to our original topic is why I think we use an eclectic mix of metric and imperial in the UK. It's what works for the vast majority, so we just go with it.