Ben Betheira tackled one of the most practical and debated questions in all of Passover law: when exactly should the Paschal lamb be slaughtered? The Torah gives a poetic instruction in (Exodus 12:6): slaughter it "ben ha'arbayim" — literally, "between the evenings." But what does that mean?
The phrase is genuinely ambiguous. Hebrew has one word for the dimming of daylight — erev, evening. But the Torah uses the dual form: arbayim, evenings plural. Between the two evenings. Ben Betheira explained that there are two distinct "evenings" in a single day. The first "evening" is the decline of the day after midday — when the sun passes its zenith and begins to descend. The second "evening" is the actual onset of night, when darkness falls.
The Passover lamb, therefore, must be slaughtered in the window between these two markers: after midday and before nightfall. This is roughly the afternoon hours, which in practice meant the lamb was slaughtered during what the rabbis would later call the time of the afternoon tamid offering — the daily sacrifice performed in the Temple.
Ben Betheira's interpretation resolved a real logistical problem. If "between the evenings" meant only the brief minutes of twilight, there would barely be enough time to slaughter, prepare, and roast the lamb before the Seder began at nightfall. By extending the window from midday onward, the ruling gave families and later the Temple priests several hours to process what could be thousands of lambs. The poetry of "between the evenings" contained within it a practical legal boundary, and Ben Betheira's reading became the standard understanding in Jewish law.