Examples:
in 2001; in January; in the morning; in the afternoon; in the evening
on Saturday; on January 20th; on weekends; on holidays; on weekdays
at 2:30 P.M.; at dinnertime; at night

Brian: Hello?
Jeremy: Hi, Brian. It's Jeremy.
Brian: Oh, hi, Jeremy. Listen. I'm having dinner right now. Can I call you back a few minutes?
Jeremy: Sure.
[ten minutes later]
Jeremy: Hello.
Brian: Hi, Jeremy.
Jeremy: Oh, hi. The Lord of The Rings is playing the Cineplex. Are you free Saturday?
Brian: What time?
Jeremy: The frist show is noon. Is that okay?
Brian: Noon? No way. weekends I sleep until 1:00. How about a later show?
Jeremy: Well, I can't make it later. But there's a show Sunday 6:00.
Brian: Sounds good to me. We can meet the bus stop 5:30.
Jeremy: Okay. See you Sunday.
Brian: 'Bye.