A weekly feature of Torah Tidbits to help clarify practical and conceptual aspects of the Jewish Calendar, thereby better fulfilling the mitzva of HaChodesh HaZeh Lachem...
Kiddush L'vana from Monday night (April 27) for the 3-day opinion and Motza'ei Shabbat (May 2) for the 7-day opinion.
This month, the earliest night for Minhag Yerushalayim comes with a little bit of a warning (some months, the warning is more serious and practical). The earliest time for KL is 7:46pm. That's almost irrelevant this month, since with sunset at 7:20-ish, it is just starting to get dark enough around 7:45. One should just be careful not to jump the gun and say KL before 7:46pm. a) because it isn't three full days after the molad until that time and b) it is not quite dark enough for ideal KL.
As mentioned, there are months when there is an issue of starting time on the first night, and other months when there is no issue at all because the molad was during the day of later at night than the Moon would be visible. And remember - Hebrew date is not the key factor - it's days after the molad.