Do production workers at large corporations work their full scheduled hours? Are there no breaks?

‌Office workers, on days when there isn't much to do, spend 7 hours pretending to work while actually slacking off, then work for 1 hour and head home, right?
For production workers at large corporations, if they are on an 8-hour shift, do they have to labor continuously for the full 8 hours?
I don't mean short 10 or 20-minute breaks,
but is it impossible to have slow days where you can sneak in 5 hours of downtime like office workers do?