When did everybody start taking ‘leave’?

We took Annual Leave when I was a Civil Servant but when I took a job in the HR department of a bank we took "Holiday" which we applied for on the form headed "Annual Leave Entitlement" but was called "Holiday Form" by all team leaders.

Now I'm on my holidays 24/7.

I remember people starting to get a ‘ winter week’ many moons ago!

My first job, in 1975, was with the N.A.A.F.I., and it was known as annual leave there. Then I went to work for British Telecom, and it was also annual leave.

I couldn't care less what it's known as, so long as I get paid for time off

I too think that 'leave' spread from the military and civil service through the public sector. I think partly that it covered other kinds of leave (see above) and partly it wasn't constrained by the specific timing of 'holidays', a term that spread from feast and holy days to be time off for the workers.
Many of us remember 'factory fortnight', which was definitely a 'holiday' and not 'leave', but when I went into the NHS I had 'leave' at different times of the year.

Holiday vs Vacation
Here in Canada we mostly call it vacation. A Holiday is a special day like Christmas or Easter which everyone gets off (or is paid extra to work). I believe etymology from Holy Day.
I currently get 30 vacation days per year.

My dh was in the Royal Navy so it was 'leave' in this house.

Locally, it's the Trades Fortnight.

My American GC have vacations.

I worked for British Gas in the 1970's and we had annual leave back then and flexi time which was brilliant.

I took leave from my job with an airline in the early 70s.
Holidays were what you maybe did when you were on leave.

I don't think it's a new thing at all..

I had annual leave in my job. OTOH Another one is 'taking a break'.
When we lived in France people often rang up to ask "Can we come to you for a few days for a break?"
It wasn't much of a break for us though.

ps my husband has always been self-employed. On the few occasions he managed to take time off he called it 'holidays'.