Epigraph from a post in the timeline "Turbocharged", a what-if in which the PC Engine avoids the misfortunes that led it to fail in the Japanese market (and the abandonment of plans for an overseas release), then becoming successful both domestically and overseas and making the NEC-Hudson...
The title of this thread is weird to me because lunar/lunisolar calendars were arguably more common in antiquity than solar ones - Ancient Greek and Chinese, for example. Even in the 19th century much of the world was working off lunar/lunisolar calendars (Islamic, Chinese, Hindu, various...
Surprised no-one's yet linked Uchronia -- that page agrees that the first work to feature alternate history is Ab Urbe Condita Libri, while the first novel-length alternate history work is Histoire de la Monarchie universelle: Napoléon et la conquête du monde by Louis Geoffroy (written in 1836)...
Re: II, you said that as 12 months are six days and six hours short of a full year and hence an extra (6-day) week was added at the end. Is there any particular way of denoting dates within that week?
Re: III, where did the one day and two hours come from? Unless I've misinterpreted your post...
There are quite a few 12*30+5 calendars out there - have a look at the Ethiopian calendar.
How can a month from July 4th to August 3rd be 30 days? Now that you've contradicted yourself I need some clarification of the month lengths.
Somehow I don't think people would find a day that is 5/6...