Departures on climbs just after midnight have been standard strategy on snow covered, glaciated peaks since the mid nineteenth century. It gets you off the route before avalanche and rock fall from sun warming makes travel dangerous. "Dark" is a relative concept, even on a moonless night, on snow and at altitude. A candle lantern was used for years to cover this kind of terrain.

There is even a standard saying for this strategy, attributed to the famous French alpinist, Gaston Rebuffat (who was renowned for his lyrical description of abominable, beastly bivouacs in the mountains)- "you will always regret starting too late, you will never regret starting too early"

It has worked for me....