From when may one recite Shema in the evening?

From the time when the Kohanim go in to eat their Terumah [produce consecrated for priestly consumption], until the end of the first watch – so says Rabbi Eliezer.

And the Sages say: Until midnight.

Rabban Gamliel says: Until the break of dawn.

It once happened that his [Rabban Gamliel’s] sons came from a house of feasting.

They said to him: We have not recited Shema.

He said to them: If dawn has not broken, you are obligated to recite it.

And [this is true] not only in this case; rather, in all cases where the Sages said that [some precept can be performed only] until midnight — their precepts are [still in force] until the break of dawn.

[For example:] Burning the fats and limbs [of the sacrifices, on the Temple altar] — their precepts [can be performed] until the break of dawn.

And [another example:] all [sacrifices] which may be eaten for one day — their precepts [of eating them can be performed] until the break of dawn.

If that is so, why did the Sages say, "until midnight"? To distance a person from transgression.

(1) From when do we read Shema in the evenings? “From the time when people come [home] to eat their bread on Shabbat (Sabbath) nights,” [these are] the words of Rebbi Meir.

And the Chachamim (Sages) say from the time when the Kohanim (priests) are able to eat their Terumah (heave offering).

A sign for this is the coming out of the stars