According to Chabad, the fast begins here:
|Alot Hashachar (dawn) | Fast Begins|
and ends as follows:
|Tzeit Hakochovim (nightfall)|
According to MyZmanim.com,
at 4:58 AM Dawn - Degrees
or at 5:07 AM Dawn - Fixed Minutes
Eating of a settled character - אכילת קבע - may not be started
during the half hour immediately preceding dawn. Please
consult your Rabbi for details.
Do not rely on zmanim times to the last moment.
Happy Yom Nikanor! This is the last fast of 2012, because the aliens are going to attack before the next (or else the war of Gog and Magog is scheduled to occur).