It goes back to jobs that give a paid lunch hour, I had that deal when I worked a service job 10 years ago. For salaried employees the lunch hour is also 'paid' and I think especially in tech where so many of us eat at desks while thinking, we're pretty justified in keeping 9-5 or sometimes even less when we know 10+ hour days are looming as teams finish big features and it's integration time.

Personally I say "9-5" a lot because it's a saying even though I'm 9-6.

9 to 5/5.30 (inclusive of an hour lunch) seems pretty common in the UK. It's also common to have flexible time, so I work 10am to 6pm most days.

In Norway the most common hours are 7:30 - 15:30 or 8 - 16, with a half hour break.