What time is prime time?

I have a friend I talk to only on weekends. She’s mostly at work during the week. She starts her day at 6am and often gets home late at night. You can call her, but be sure she won’t be with her phone when she’s at work.

We are both friends to someone who starts the day at 3am, does most things until they step out at 8am and returns home so they can sleep at 6pm. Only to wake up at 2:30am to prep for the day. Like clockwork.

I have another friend who also starts her day at 6am and takes a break by 9:30am. I know not to call her between 10am and noon because she will be sleeping. Then she starts the second part of the day and retires to bed later at night.

When I talked about these my friends recently, someone I barely knew scolded: “how can she be wasting prime time sleeping?”

Made me wonder who defines what time is prime time.

None of their approaches are right and wrong. Just different.