Flight times from various places to Korea?

What is the average flight duration from New York to Korea?
How about Minnesota to Korea?
And then finally England to Korea?

I need general flight times, just to be somewhat correct in a fanfic I'm writing. I also need the times I would have to leave to get to Korea at 9:30AM from New York, 10:00AM from Minnesota, and 9:00AM from England.

If you can only give me the first part, I'd be happy with that. But doing the math when crossing timezones is kinda hard for me xP

Thank you very much, simoncp!

- Depart New York (JFK) on Korean Airlines at 14:05, arrive the following day in Seoul (ICN) at 17:35 after a flight of 14h 30m.

- Depart Minneapolis (MSP) on Northwest Airlines at 15:05, arrive the following day in Tokyo (NRT) at 17:15, before connecting to a Northwest Airlines flight departing Tokyo (NRT) at 18:50, then arrive into Seoul (ICN) at 21:45 after travelling for 16h 40m.

- Depart London (LHR) on Asiana Airlines at 21:00, arrive the following day in Seoul (ICN) at 16:40 after a flight of 10h 40m.