Here for some reason they run them mostly during the daytime hours, that is the short under a few hundred kilometres trains. Perhaps it is because maintenance is so bad that they need the daylight to fix the trains when they breakdown, ask just about any traveller whom has been on Amtrak.
I maybe mistaken, but I heard the entire journey from Sankt Peterburg to Vladivostok takes 8 days(and nights) It is an 8 day journey I long to take so I can see the Motherland.
Here in the USA during the 1920's there was a train and plane service called TAT which flew people on planes during the day and then put them on trains at night, it was thought safer because night time flying in the 1920's was much more dangerous in the pre instrument flying era.
Dave