The additional leap second will be inserted at 00:00:00 UTC tomorrow,
July 1st.
That corresponds to 10:00 in the morning Australian Eastern Standard Time.
The sequence of dates of the UTC second markers will be: 2015 June 30, 23h 59m 59s 2015 June 30, 23h 59m 60s 2015 July 1, 0h 0m 0s.
The leap second can be "heard" on shortwave on WWV and WWVH.
It
might be "observable" on the NIST US Government time web site -
http://www.time.gov/
Some of the US stock exchanges, including the NASDAQ, will be intentionally closing
down prior to the insertion of the leap second -
http://www.nasdaq.com/article/market...20150518-01174
In 2012, the Qantas Amadeus booking system crashed when the leap second
took place delaying 400 flights -
http://www.theguardian.com/technolog...-qantas-reddit