On winter evenings

[Brahman]

I found the following sentence in a book by Selina Hastings:

1. Afterwards on winter evenings there was sometimes a game of whist...

is there a reason why she has used "on" instead of "in"?

[SARDORBEK]

Hi, Brahman! In my country (Uzbekistan) English is taught as a foreign language.
As we know, there is an expression  in the morning and in the mornings
In the same way

In the afternoon & in the afternoons
In the evening & in the evenings

But if there is an adjective before these expressions, as far as I know,
the preposition “in” should be normally turned into “on”

For instance:

On Monday evening(s)
On Friday afternoons(s)
On Sunday evening(s)

For my money (<-- it’s an idiom that I learnt on Englishclub.com),
Selina Hastings has said “on’...
I hope this answers your query!

Respectfully,
SardorBEK