Question about time period transition points

[Adam Vartanian]

> Phrased differently, for the Americas/NewYork transitions this spring:
> 1) Is the time coordinate value at the instant of transition "2:00 AM" or "3:00
> AM" (NIST says "begins at 2:00 a.m. on the second Sunday of March")
>
> 2) Is the designation of that coordinate (in the local New York City timezone)
> "EDT" or "EST"?

At least in the United States, time transitions from 1:59:59 AM EST to
3:00:00 AM EDT.  I don't know if other countries have different rules,
but it would be surprising to me if they did.

- Adam