The last time we had a leap second was 1998. This is exciting! We're going to have another one.
For me this will occur Dec 31, 7:00pm EST. Unlike the New Year, the whole planet experiences this transition at once, when the UTC clock ticks 23:59:60.
Below, is what the last leap second looked like in 1998
Date Time TAI NTP Leap NTP Seconds
1. Dec 31 98 23:59:59 31 01 3,124,137,599
2. Dec 31 98 23:59:60 31 01 3,124,137,600
3. Jan 01 98 00:00:00 32 00 3,124,137,600
4. Jan 01 99 00:00:01 33 00 3,124,137,601
By the way, this is the 23rd leap second. Yes, I know what you're thinking. The number 23 is interesting because it's the first intersection of Pi and e.
Pi = 3.141592653589793-23-84 e = 2.718281828459045-23-53
Also, the earth is tilted at 23.5 degrees...hmm there's that number again. Ramsey Theory? Maybe, probably.