Since 140 AD scientists have attempted to break down the hours in the day into a consistent and accurate means of measure, but measurement of the 24 hour day is not an exact science. One minute has 61 seconds when a leap second is added every now and then, in order to synchronize atomic clocks with the Earth's slowing rotation. Scientists don't always make adjustments, but, when they do, it’s done on either June 30 or December 31, or "Leap Second Time Adjustment Day".
If we didn’t add an extra second to the clock, sometime a few million years from now, humans or their descendants will sleep till noon. But for now, it’s a real stress on may business who worry their websites may crash — and Google’s trying to block it.
Cool!!! - Clock enthusiasts take note: A leap second has been scheduled for June 30, 2012. A leap second is an adjustment to the atomic clock-based Coordinated Universal Time (UTC) to bring it more closely in line with Universal Time (UT), which is based on the rotation of the earth. The two time standards do not agree because the earth’s rotation is ever so gradually and unpredictably slowing down. Yes, really.