Why is 5 o’clock drinking time?

Many people have their own drinking times. I think it's ridiculous, but some people even drink at breakfast. But the general consensus is that five o'clock is the ideal time to start drinking. So why is 5 o'clock drinking time? Are you an evening drinker or a breakfast drinker?

Why is 5 o’clock drinking time?
Why is 5 o’clock drinking time?
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