How much of my flight will be in the dark? please answer?

I can't really say but I can tell you that they will make it dark inside of the plan for much of it. Russia is 8 hours ahead of DC, so the plane ride is about 10 hours. I will tell you that since you are landing in Russia in the morning and leaving DC in the afternoon they will make it very dark inside so that people can sleep. Whether it is day time or night time it shouldn't matter.