Charles Spurgeon Commentary Exodus 12:6

"and ye shall keep it until the fourteenth day of the same month; and the whole assembly of the congregation of Israel shall kill it at even." — Exodus 12:6 (ASV)

And you shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening.

Just as the sun went down, or just before it set for the evening.

There is also the marginal reading "between the two evenings." The evening before the sun set, was the first, and then the daylight after the sun set was the second evening.