Modern Jews cling to the rabbinical view that the lamb was to be slaughtered near the end of Nisan 14, between the time when the sun began to descend (about three o’clock) and the actual sunset. As a result, they hold their Seder after sundown, when Nisan 15 has begun.​—Mark 1:32.

23. Why are months added to the Hebrew calendar, and how is this handled by modern-day Jews?

²³ Another reason why our date may differ from that of the Jews is that they employ a predetermined calendar, which system was not fixed until the fourth century C.E. Using this, they can set dates for Nisan 1 or for festivals decades or centuries beforehand. Moreover, the ancient lunar calendar needed to have a 13th month added occasionally so that the calendar would synchronize with the seasons. The current Jewish calendar adds this month at fixed points; in a 19-year cycle, it is added to years 3, 6, 8, 11, 14, 17, and 19.