In chapter 6, "The Journey From Platform Nine and Three-Quarters", it states that the Hogwarts Express departs from King's Cross in London on 1 September at 11:00. At the end of the same chapter, it states that by the time the train arrives at Hogsmeade Station, it's getting dark.

The best source we have for the location of Hogsmeade is the Prisoner of Azkaban movie, which states that it's near Dufftown in Moray; and J. K. Rowling was a script consultant for the movies, so we can presume this information to be canon. According to sunrisesunset.com, on the 1st September in Moray sunset is 20:11 and it doesn't start getting dark until 20:52. Also, Wikipedia states that Dufftown is 430 miles from London; the train must be very slow for a train, or take quite a roundabout route, if it takes about 10 hours (an average of less than 45 MPH) for the journey.