[tz] the final second before standard time daylight savings time transitions

Hello, Is there any official documentation on the time zone for March 13 2016 in New York City, when the clock says 1:59:59.99991000 ? My guess would be that it is EST or -04:00 offset, but I cannot find anything that discussed the fractions of the last second. We store fractions of seconds, and we need to be able to convert to a particular offset. Thanks for your work and your consideration. P.S. I have enjoyed the notes in the time zone rules. Most Respectfully, Mark Inman Army Analytics Group Email: mark.h.inman2.civ@mail.mil Personal Work Phone: 707-863-7150 Personal Cell Phone: 925-324-9864 Personal Cell Text: 9253249864@vtext.com