in the afternoon
I usually sleep in the afternoon.

on + day of the week + afternoon
I have a job interview on Tuesday afternoon.

on + day of the week + afternoons
Our group meets on Tuesday afternoons.
(=every Tuesday afternoon)

on the afternoon of + date
He was born on the afternoon of April 1,1995.

on the afternoon of + event
He was there on the afternoon of the incident.

this/yesterday/tomorrow + afternoon
I met her yesterday afternoon.

early/late + afternoon
It was late afternoon when she left.