Every 5000km, or 3 months, whichever comes first.  PERIOD.  Doesn't matter what it says on the oil bottle, there are no motor oils that can prevent condensation in your engine, and condensation is water, water is not a lubricant.  I have been an automotive technician for over 30 years, and the number one reason for engine failure is infrequent oil changes.  Pay me a little now, or a whole lot later.  You decide.