Was I Out When

[weecalf]

People started saying back in the day instead of back in the days ?

[Mamyalynne]

When did you come back in?

[weecalf]

Last Thursday week 2 months ago to the year .

[Mamyalynne]

That'll be it then.

[JimF]

When did people ever say "back in the days"?

[wolf63]

I've only heard it on American TV. It sounds stupid.

[bobbinwales]

Back in the day we used to say 'in the olden days' or 'days of old' or 'in the good old days'

[Buenchico]

Were you out in 1910 then?

From the OED:
https://ibb.co/n85chYd

[gingejbee]

I'd use "back in the days" if I was following it with "when such-and-such happened".
I'd use "back in the day" to mean "long time ago" generally, without specifying any particular thing.

[weecalf]

All the time I think I would still say back in the days as it relates a period of time not just wan day .

[Mamyalynne]

'Days of yore' is so much more poetical.

[weecalf]

Thought it ment a time we remembered in our live back in the days when I was .

[Lie-in King]

It was all fields then...

[piggynose]

Isn't back in the day a london form of back in the days? As it sounds ridiculous imho.

[JimF]

"From the OED"

Exactly. All six quotations cited say "back in the day", not "back in the days".

[Mamyalynne]

'The day' can refer to a period of time - eg 'Jazz was the music of the day', 'Mini skirts were the fashion of the day'.