You live in the EU (or a country that has the same rules for summer/winter time as the EU). 2013-10-27 was 25 hours long in such places, because the clocks wen

You live in the EU (or a country that has the same rules for summer/winter time as the EU). 2013-10-27 was 25 hours long in such places, because the clocks went back. A bare date is assumed to be midnight, and adding 24 hours only gets you to 11pm in this case. The bug is in your code, not in PHP. I don't know whether PHP has functions for date arithmetic (as distinct from time stamp arithmetic, which you are using). Alternatively you could try using UTC, or some other timezone that lacks summer/winter time.