need "at" or omit "at"?

[Zoe2008]

we shall send you the document before 18:00 "at" Korea time

[Bennevis]

Тhey don't use "at".

for example,
6 PM Eastern Standard Time.

[bhaisahab]

we shall send you the document before 18:00 "at" Korea time

You don't need "at". I would say "Korean time".

[sunsunmoon]

Are
- Chinese time, not China time
- Australian time, not Australia time
- French time, not France time
correct?

[emsr2d2]

Are
- Chinese time, not China time
- Australian time, not Australia time
- French time, not France time
correct?

Yes.

[sunsunmoon]

Are
- New Zealand's time, not New Zealand time
- Sydney's time, not Sydney time
correct?

[emsr2d2]

Are
- New Zealand's time, not New Zealand time
- Sydney's time, not Sydney time
correct?

No.

We change the name of the country to whatever is used for the name of the nationality for the adjective.

Where there is no such version, we just leave the name of the country of city. Here is a selection, incorporating both types:

2pm Chinese time.
2pm Dutch time.
2pm British time.
2pm UK time.
2pm London time.
2pm New Zealand time.
2pm Canadian time.
2pm American time (though bear in mind there are various time zones in America, so you will be using something like "Eastern Standard Time".)
2pm Hong Kong time.
2pm Italian time.

[sunsunmoon]

emsr2d2,

Thank you very much for going to the trouble of giving several examples. I hope they are of great help to Zoe too.