I am not a teacher.
They should both start with a capital letter and end with a full stop. Also, pm is written p.m.
Apart from that, both versions (with or without 'out' which I think was the point of your question) are possible although I wouldn't say, '…this afternoon at 4 p.m.'. It's tautologous since p.m. means 'after noon'.
Student or Learner