Which website should I follow for Halachic times?
I’ve noticed there is always a significant time difference when I compare the time of tzeis hakochavim on myzmanim.com versus on chabad.org.
Can you explain why this is, and which site is accurate?
The reason for the difference is due to the various opinions on how to calculate this zman; both websites include many opinions while choosing one to use as its default. (On chabad.org you can click on “Additional Zmanim” to see the other opinions. On myzmanim.com you can click on the green arrow pointing down to see them.)
In practice, you may rely on the “default zman“ on Chabad.org.
See also here:
1. What would be preferred, to Daven Maariv early with a Minyan (in a case where one Davened Mincha after Plag), or to Daven Beychidus after Tzeis? 2. In general from what time can one start Davening Maariv Lechatchila?
My Shul is in Boro Park (11218); what time should we Daven Maariv Leil Purim?
Listen here for an analysis of some of the issues (Hebrew):