June 30, 2015 23:59:60

AWS Official Blog covers the upcoming leap second shenanigans in “Look Before You Leap – The Coming Leap Second and AWS“:

The International Earth Rotation and Reference Systems (IERS) recently announced that an extra second will be injected into civil time at the end of June 30^th, 2015. This means that the last minute of June 30^th, 2015 will have 61 seconds. If a clock is synchronized to the standard civil time, it will show an extra second 23:59:60 on that day between 23:59:59 and 00:00:00. This extra second is called a leap second. There have been 25 such leap seconds since 1972. The last one took place on June 30^th, 2012.

Not all applications and systems are properly coded to handle this “:60” notation.