Can a brocha be corrected?

A person who recited the wrong brocha but corrected himself within the span of toch kdei dibur (the time it takes to say “sholom alecha rebbi”) has fulfilled his obligation. If he delayed longer, even if he was thinking about how to correct himself, he is not yotzei. Likewise, if he began another brocha he is not yotzei.

סעיף ב, ס"ק ו-ז, וביה"ל ד"ה ונזכר וד"ה אם; ביאורים ומוספים 1-3

How soon must the correction be made?

As mentioned, the amount of time within which one can correct a mistake is the interval that it takes to say three words. There are some opinions which extend the period to include another word. Although the basic halacha does not follow this opinion, there are times that it can be relied upon. For example, during Ma’ariv on Friday night there is a different ending to the brocha of Hashkiveinu than that which is ordinarily recited during the week. If a person accidentally recites the weekday text, he is still yotzei, but he can correct his mistake if he does so within the time it takes to say four words.

ביאורים ומוספים דרשו, 1 ;וראה שם, 5

Which part of a brocha must be mistake-free in order to be yotzei?

The following halachos apply if someone confused the evening and daytime brochos of Shema: Shulchon Aruch rules that in order to be yotzei, it is necessary to have recited the correct text at the beginning or in the middle of the brocha and also at its end. If one did not say the correct text at the beginning or middle, he is not yotzei--even if he corrected himself at the end. Likewise, if the end was not correct, one is not yotzei even if the beginning was mistake-free. Others hold that the only factor necessary to be yotzei is the correct recitation of the text at the end.

סעיף ב, ס"ק ג, ד ו־ח, וביה"ל ד"ה ולא; ביאורים ומוספים דרשו, 6

• If circumstances prevented a person from being able to recite the nighttime Kriyas Shema before daybreak, he may say it b’dieved until hanetz hachamah. The brochos, except for Hashkiveinu, may also be recited.

• A person who did not read Kriyas Shema at the proper time can still say it, along with its brochos, until the fourth halachic hour of the day. Although the time for Shema has passed, the brochos are not directly connected to Shema and may be said for an additional hour.

• If a person mistakenly missed a tefillah, he can do a tashlumin (a make-up tefilla) during the next time for tefillah. Some Rishonim apply this concept to Kriyas Shema. They say that if a person missed saying Shema, he should recite it twice when the time comes to say it again. 

• Which brochos may be fulfilled by listening?

• How did the Rosh change the custom of Birchos Kriyas Shema?

• Can an individual recite Kedusha on his own?