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Verified manually that the following quickly fails the assert on Windows but passes with this commit:

I am unable to reproduce such success on Linux?

Merged, thank you for your contribution!

@vstinner out of curiosity does it work for you, it's hard to believe it's somehow windows only.

@vstinner out of curiosity does it work for you, it's hard to believe it's somehow windows only.

Using a debug build, I failed to reproduce the issue. I trust the code, I know what it does :-)

Huh; I can still reproduce the problem but only on a release Linux build. I'm investigating to see if there's something else I can do to ensure consistency there.

start = time.time()
end = datetime.datetime.now()
start = datetime.datetime.fromtimestamp(start, None)

time.time() uses float which is not great in terms of accuracy. Using time.time_ns() would be better. Sadly, there is no "fromtimestampns()" function.