Care to point out which hours that would be? Unless there's a timezone that skips 12 hours or more on DST, I don't see there's a problem. Had ramjamman actually suggested to subtract 86400 in each iteration, there would be 6 hours/year where this would be a problem - the hour between midnight and 1 AM on the Monday - Saturday following the Sunday when DST is enabled. (Assuming DST skips an hour, and starts on a Sunday. And assuming the local timezone actually has DST - many parts of the world don't).