Until when during the day may one recite Birchas Hashachar?
Initially, one is to recite Birchas Hashachar early in the morning, in close proximity to awakening. If one did not do so, the blessings may be said throughout the entire day [up until sunset]. Furthermore, some Poskim rule it may be said even at night, up until one goes to sleep. However, some Poskim argue that it may not be said the entire day and conclude that it may only be said until the 4th hour of the day [i.e. Sof Zman Tefila]. Other Poskim conclude that it may at the very least be said until midday, and those who say it until sunset are not to be protested. Practically, one is initially to be careful to recite the blessings as early as possible, and in the morning, although if this time was missed the blessings may be said up until sunset.
 See Admur 46:2-3; 71:1; Sefer Hasichos 1904 p. 20; Igros Kodesh 19:390; 18:277; Shulchan Menachem 1:6
 Ketzos Hashulchan 5:7 based on Admur 52:1 which does not place a time limit on the allowance of saying Birchas Hashachar after Davening; Setimas Kol Haposkim who mention no time limit in their ruling that [Biur Halacha 53:1 “Kol Habrachos”]; Machatzis Hashekel 71:1; Mamar Mordechai, Nehar Shalom and Gr”a, brought in M”B 52:10; The M”B ibid concludes that one who relies on these opinions is not to be protested.
The reason: As the custom today is to recite the blessings based on the pleasures of the world [and not one’s individual pleasures] and there is thus no reason to limit these blessings to the morning. [See Biur Halacha ibid]
 Gra in Maaseh Rav brought in M”B ibid
 Derech Chaim Onen 4 based on M”A 71:1, brought in M”B ibid and negated in Biur Halacha 53:1 “Kol Habrachos”
 Mishneh Berurah 52:10 that initially it should not be delayed past the 4th hour, although Bedieved may be said until midday, as so is proven from many Achronim [Levushei Serud, Chochmas Adama, Shulchan Shlomo, brought in Biur Halacha ibid], and those who are lenient even past Chatzos are not to be protested;
 M”B ibid
 See Biur Halacha ibid who at first writes that one may/should be lenient even after midday, but then concludes only that one who is lenient after midday is not protested. Practically, from the Setimas Haposkim one may be lenient until midday