As a kid, I can remember advertisements for TV shows on the 3 networks that existed in the 70s.
Whenever they mentioned a time, it was always (x) O’Clock, (x-1) Central and Mountain.
I always took this to mean that it was on at 8:00 eastern time, 7:00 central time, and then was delayed 1 hour for Mountain and then delayed 3 hours for Pacific.
Now, I only see 8, 7 Central and they never mention Mountain or Pacific. Does that mean it comes on at 8:00 Mountain and Pacific, meaning it’s delayed 2 and 3 hours respectively? Or has it not changed but they don’t bother mentioning Mountain because there’s a relatively low population (or at least low population density) in most of that time zone?