To refer to one point in time, use the prepositions "in," "at," and "on."
Use "in" with parts of the day (not specific times), months, years, and seasons.
He reads in the evening.
Use "at" with the time of day. Also use "at" with noon, night, and midnight.
She often goes for a walk at night.
Use "on" with days.
I work on Saturdays.