In Engpsh, you can say "the afternoon class" or "the class in the afternoon." If you want to be more specific about the time, you can say "the class at 2:00pm" or "the class at 3:00pm," etc. It's also common to use the word "pm" (short for "post meridiem") to refer to the time in the afternoon, so you could say "the class at 3:00pm" or "the class at 3:00pm in the afternoon."