233. The Time to Recite the Evening Shema

Kriyas Shema 1:9

The obligation to recite Shema at night takes effect at the time when the stars appear. If a person delays – which he ought not do – he can still fulfill his obligation if he recites Shema by dawn. A deadline of midnight was established in order to help keep people from erring in this matter.

Kriyas Shema 1:10

If a person recites the evening Shema after dawn but before sunrise, he does not fulfill his obligation unless circumstances beyond his control prevented him from doing so earlier, such as if he were drunk or sick. If a person is prevented by circumstances beyond his control and recites Shema at this time, he does not recite the blessing “Cause us to lie down….”