That’s true, but you still have to know much less information. In most cultures, most people eat the main evening meal somewhere between 18h and 23h; Southern Europe tends later in that range than most places, whereas the US tends earlier. This is still a lot simpler than each longitude having its own unique offset that can range anywhere from -12 to 12.
If you visit Spain as a tourist and eat at 19:00 local time every day, you’ll be slightly out of sync with the locals but you aren’t going to cause any huge drama. If you never even learned the fact that Spanish people eat later, you’d still basically be fine. So knowing that cultural fact about Spain isn’t absolutely essential the way it would be to learn the offset of each place in a world without time zones.