"Dusk, to his mind, was the hour of defeated." Explain?
To understand what the author is saying, go a little past the line that you mention. There, you will see him explain the meaning of this line.
What the author is saying is that dusk is a time when the poor people, the people who have "lost" in the competition of life come out. They come out at this time because they can conceal how bad off they are. They can come out in the soft light and hope that people will not notice how poor they are or, at least, people might not recognize them.
So the darkness at the dusk is camouflage for people who are embarassed about their lives and do not want people to notice them. Here is the important line:
Men and women, who had fought and lost, who hid their fallen fortunes and dead hopes as far as possible from the scrutiny of the curious, came forth in this hour of gloaming, when their shabby clothes and bowed shoulders and unhappy eyes might pass unnoticed, or, at any rate, unrecognised.
the defeated or the unsuccessful people come out at the time of dusk so that people do not notice them or may be they pass unrecognised.
it is the time when the defeated people who hide their misfortunes and dead hopes from the curious thought of man can come out from their homes where they find themselves less defeated.
thus dusk is the hour of the defeated.