The issue of changing day and night is indeed a very important one!
Dividing heroes and units into daytime and nighttime ones opens up new gameplay possibilities.
I have been thinking about this for a long time. For now, the best solution seems to be to make a day last 2 weeks (14 game days/turns). That is, 5 days of daylight, 5 days of darkness, with 2 days each of morning and evening in between.
All sorts of jokes about eclipses and leap years are generally welcome!
However, it would be better to abolish the days of the week altogether. Let there be separate holidays assigned by the map developer's script.
Issue #62 about Day and Night Change has been released! Read it here!