On days when Hallel is recited – such as the eight days of Hanukah – during which period of the day is one required to recite it?
Hacham Ovadia Yosef, in his work Hazon Ovadia (Laws of Hanukah, p. 230), rules (listen to audio for precise citation) that Hallel should be recited at some point between sunrise and sunset. If one recited Hallel earlier than sunrise, then he has nevertheless fulfilled his obligation, provided that he recited it no earlier than "Amud Ha'shahar," or daybreak, which generally occurs approximately 72 minutes before sunrise. (In all such cases, one should consult a reliable Jewish calendar for the precise time of "Amud Ha'shahar.")
If a person did not recite Hallel throughout the day until after sunset, then he may still fulfill his obligation by reciting it during the period of "Ben Ha'shemashot" (twilight), which extends for approximately 13.5 minutes after sundown. Hacham Ovadia Yosef (ibid. p. 231) explains that this Halacha is based upon the ruling of the Rambam that the Hallel recitation is an obligation enacted by the Sages, and does not constitute a Torah requirement. As such, we may apply here the famous principle of "Safek De'rabbanan Le'hakel," which allows one to assume the more lenient possibility when faced with a situation of doubt concerning a Rabbinic obligation. It is uncertain whether Halacha considers "Ben Ha'shemashot" as part of the daytime or as nighttime, and hence with regard to the Rabbinic obligation of Hallel, we may assume it to be daytime and thus allow reciting the Hallel. Nevertheless, Hacham Ovadia Yosef rules that in such a case one should omit the Beracha, as a Beracha should never be recited in situations of doubt.
It is forbidden to speak during the Hallel recitation. Nevertheless, if one hears Kaddish, Kedusha or Barechu as he recites Hallel, he is permitted to respond. Similarly, one may answer "Amen" to a Beracha he hears during his recitation of Hallel. However, one may not answer "Amen" after he recited the introductory Beracha to the Hallel but before he began reciting the Hallel itself. It often happens that after reciting the introductory Beracha one hears somebody else completing his recitation of the introductory Beracha. If one had yet to begin the actual recitation, he may not answer "Amen" to the Beracha, and, if he does, he must repeat the Beracha. This is comparable to a case addressed in the work "Panim Me'irot" (vol. 2, Siman 5) of a person who recited the Beracha over wine and before he drinks he hears somebody else reciting that same Beracha. The "Panim Me'irot" ruled that in such a case one may not answer "Amen" to the Beracha he hears before he drinks. Similarly, one may not answer "Amen" to a Beracha he hears in between his recitation of the introductory Beracha to Hallel and the beginning of his recitation of the actual Hallel. This is the ruling of the "Erech Ha'shulhan," as well as of the Hid"a (Rav Haim Yosef David Azulai, 1724-1807), in his Birke Yosef (213:5), and this is the position accepted by Hacham Ovadia Yosef.
If one hears Kaddish, Kedusha, Barechu or a Beracha after he completed the Hallel recitation but before he began the concluding Beracha of "Yehalelucha," he may answer "Amen" (Hazon Ovadia – Laws of Hanukah, p. 226).
Summary: Hallel must be recited between sunrise and sunset, though if one recited it before sunrise he has nevertheless fulfilled his obligation, provided that he recited it after daybreak. If one did not recite Hallel before sundown, he may recite it without a Beracha for a period of 13.5 minutes after sundown. One may respond to Kaddish, Kedusha and Barechu, and answer "Amen" to a Beracha," during the Hallel recitation, even if he had completed the Hallel but has yet to begin the concluding Beracha of "Yehalelucha." One may not, however, interrupt even for this purpose if he had recited the introductory Beracha to Hallel but has yet to begin the actual Hallel recitation. If he did interrupt, even to respond to Kaddish and the like, he must repeat the introductory Beracha.
