Here's another stab at the 'holy grail'. I'm using a combination of the Little Bramper developed by Thomas Bethel and the Aperture Drive custom built by Andrew Curtis. NOTE: Absolutely no de-flicker techniques were used in this clip! IMHO this is the real deal way to flawless transitions from day to night. I can get well over 20 stops of silky smooth sliding latitude with this system!

Here's some linky:
Little Bramper: timescapes.org/phpBB3/viewtopic.php?f=28&t=1893
Aperture Drive: timescapes.org/phpBB3/viewtopic.php?f=4&t=2442&p=15717