I missed that you are proposing fraction-of-day instead of microseconds.
Fraction of day is how RD/JD are usually defined as you know so there is familiarity and a lot of literature to support this approach.
I recognise better now why you were emphasising that precision is important - in order to preserve round trip conversions of at least microsecond resolution i assume, since that’s the contract described by Calendar.
I’ve done most of the work now to update my PR - pending whether there’s a consensus on whether to go the microseconds-since-midnight or the fraction-of-a-day route.
@Qqwy, @josévalim any additional thoughts to arrive at a conclusion before i finish up the next version?
