I say it was early September. The tune Hot Town Summer in The City was the perfect song to open. NYC was really the movie's main lead not Bruce or Samuel L.
Tell you what…When I send my ex-wife her money…you can lick the stamps.

𝙽𝚈𝙲 []

The intensity of the sun gave that fact up.
That too.

The summer was the season. The intensity of the sun gave that fact up.

𝙽𝚈𝙲 []

Looks like summer by the sweat on McLean though.
Wow, really? How about all the trees with green leaves on them?

He didn't mean it was literally Christmas. He meant it was like a holiday because there were no cops around so it's Christmas for the thieves since they wouldn't get caught.

No. It's impossible to be that stupid.

Early to mid September. It's clearly hot outside but kids have already gone back to school.

When McLean stops the shoplifting kid on his bicycle, the kid says " It's Christmas you could steal city hall!"
Looks like summer by the sweat on McLean though.
Using "It's Christmas" in that context was just a way of saying (in relation to his stealing of all the candy) it's easy as all the police are doing something else.
Not that it was actually Christmas.
And so, God came forth and proclaimed widescreen is the best.
Sony 16:9

I took it as late summer or early fall. The reason being that the department store said "Back to School Sale" on the outside.
All I need is one mic

The kid didn't mean that it was Christmas time. He's talking about that it seems like Xmas where you get a lot of gifts, which is what was going on at the time, due to the heist.

The opening song says it all. "Hot town, summer in the city."

And McClane mentions an Indian summer at some stage, so it is late summer, early autumn.

When McClane goes into the federal reserve, as he approaches the lift with the guard they exchange words and the guard says 'what do you think of this heat, feels like its going to rain dogs and cats', I'm guessing late summer.

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