tzais
This method returns tzais usually calculated as 40 minutes (configurable to any offset via .setAteretTorahSunsetOffset) after sunset. Please note that Chacham Yosef Harari-Raful of Yeshivat Ateret Torah who uses this time, does so only for calculating various other zmanai hayom such as Sof Zman Krias Shema and Plag Hamincha. His calendars do not publish a zman for Tzais. It should also be noted that Chacham Harari-Raful provided a 25 minute zman for Israel. This API uses 40 minutes year round in any place on the globe by default. This offset can be change by calling .setAteretTorahSunsetOffset.
Return
the Date representing 40 minutes (configurable via .setAteretTorahSunsetOffset) after sea level sunset. If the calculation can't be computed such as in the Arctic Circle where there is at least one day a year where the sun does not rise, and one where it does not set, a null will be returned. See detailed explanation on top of the AstronomicalCalendar documentation.
See also
.setAteretTorahSunsetOffset