Booked J fare for Japan in late September 2013. Decided to pay it in Oct, got error message saying; please call Istanbul. Noticed that departure time was changed by 5 min and needed my confirmation. And my guess went right. During long taking call agent helpfully took my 5 min schedule change confirmation and updated the J fare to same day´s current fare at J booking class. That was 2 x 600€ more (2 pax). So lesson learned, if you book pay later option, pay it asap. This flight is no go for me, will look another carrier.