The City That Sleeps Sometimes
The poor and working class are often too tired from a day of work to stay up late at night. That, with the expense of oil for night time light, prevents most from doing much but working through their days and sleeping through the night. Of course, the some of the young sneak away to secret gatherings (like concerts with illegal music) to drink stolen alcohol and discuss new and rebellious ideas.
The upper class, by contrast, spend their nights at parties and other social functions. Trains run at all hours, and it is not unheard of for those currently in higher education to sleep during the day and stay out all night.