Back in the day

[Benjamin Barrett]

I'm still not 100% satisfied with the scope of this expression.

Would it be correct to say:

1) Back in the day, the Romans were the best builders of plumbing
around.

2) Back in the day, Noah built the ark. (Does this depend on
believing in Noah and his flood?)

3) Back in the day, Hercules completed his tasks.

4) Back in the day, cows were domesticated.

5) Back in the day, fire was discovered.

6) Back in the day, mammals came into existence.

Benjamin Barrett