I hope you are partying like its 1999 (again) tonight, cause the headless chooks are out and about prophesizing doom as a leap second is added to clocks.

One second is being added at 11.59 and 60 seconds (the final minute will be 61 seconds long)

here's one newspaper's first paragraph ....

Airlines, trading floors and technology companies are braced for chaos today as world timekeepers prepare to add a leap second to global clocks.

Yeah, yeah. We're all doomed. Again.

It will have some impact on markets ... here's the CME. They are delaying the opening of Globex.

(Bolding mine)

To account for the leap second, an extra second that will be added to Coordinated Universal Time (UTC) on June 30, 2015, CME Group is delaying the CME Globex market open for trade date July 1.

Tuesday, June 30 (trade date Wednesday, July 1)
Pre-open for all markets will begin at 19:30 CDT
All markets will open at 19:45 CDT