  Where flying isn't concerned, it isn't the length of the flight that matters... only the difference in time zones. Flying from Paris to Johannesburg, while it might take you 00-00 hours, wouldn't leave you very jetlagged because there's only 0 hour time difference. A flight from New York to Tokyo, on the other hand, leaves you with a 00-hour difference, which effectively means reversing your sleep/wake schedule.  