According to the Gaon when is Tzet HaKochavim in N.Y. and N.J.?

ב"ה Shalom The opinion of the Gra, whom I assume you are referring to as the Gaon is that is Tzet HaKochavim 3/4 of a "Mil" after sunset. Rav Moshe Feinstein zt"l deals with this in detail in a Teshuva. שו"ת אגרות משה אורח חיים חלק ד סימן סב. If this is accepted in all communities in New York and New Jersey, is something I suggest you take it up with your local Rabbi. The issue is also discussed in a sefer called מאבני המקום, סי' א , פרק ז. All the best