Every salary job I've worked is 8 hours a day of work with a 1 hour unpaid lunch. So it's something like 08:00-17:00 or 09:00-18:00 as your work hours. That's what is called 40 hours a week around here. You could consider that 45 hours a week. As lunch is unpaid that's considered your time to do whatever you want including leaving the job site for that hour.

Some shift-work places will do something like 09:00 to 17:00 with a paid 30 minute lunch. Since lunch is paid time, they can require you stay on the job site. This is isn't as common now as it used to be, but some places like factories that run a 24 hours a day schedule still do things like that.