Halachos for Erev Shabbos Kodesh

1) The sun's cycle is a 28 year cycle. Once every 28 years , always on a Tuesday evening, the sun returns to the exact spot where it was on the day that Hashem created it on "the fourth day of creation".  (The next time this will happen is in  the year  5,797-2037)

Since we cannot see the sun at night, we postpone the blessing until the following morning, thus "Birchas HaChama" always takes place on a Wednesday morning.
 

To commemorate this phenomenon, the Bracha of "Baruch Ata Hashem Elokeinu Melech HaOlam Oseh Ma'asei Vereishis" is recited when the sun is seen at that time, along with some other special prayers. (Talmud Brachos 59b, Shulchan Aruch Orach Chaim Siman 229:2)

The earliest time for this Mitzvah to be performed is after sunrise (Netz Hachama) and only after the entire "ball" of the sun is visible.

 
The latest time for reciting this Bracha is a subject of debate in the Poskim.

 
Some Poskim maintain that you only have until the end of 3 Halachic hours into the day (same as  Sof Zman Krias Shma. See Shu"t Chasam Sofer Orach Chaim Siman 56 and Mogen Avraham 229:5)

Other Poskim maintain that one can perform this Mitzvah throughout the entirety of the day. (Elya Rabbah 229:2 and others. However, even according to those opinions, L'Chatchilah it should be recited before Chatzos. According to the Mishna Berura 229:8, it may be recited with Hashem's name until Chatzos, and only without Hashem's name after Chatzos)

According to all opinions, it is best to say the Bracha as early as possible and not push it off for no reason until close to the deadline.

 
2) It is best to perform this Mitzvah with a large group, B'Rov Am Hadras Melech, therefore if you will only have a group after Shacharis, according to many Poskim it is best to do it then, rather than doing it alone at Netz HaChama. (Shu"t Chasam Sofer ibid. and Elya Raba ibid.)

Other Poskim contend that it is better to recite the Bracha immediately upon seeing the sun and not to wait to do it together with a Tzibbur. (Kitzur Shulchan Aruch Siman 60:6 and 7, Kaf HaChaim Siman 229:13 and 14 and others)

The prevalent minhag in many Jewish communities is to daven Shacharis K'Vasikin and then recite the Birchas HaChama together as a Tzibbur.

Halachos for Shabbos Kodesh

 
1)Some Poskim maintain that women may say this Bracha like any other Mitvas Asei SheHazman Grama (such as Lulav, Sukkah etc. and similar to how they say the Bracha over thunder and lightning) where even though they are not obligated, they may do it if they like.(Rav Moshe Feinstein Zatzal ruled this way)

 
Other Poskim maintain that they should not recite the Bracha , rather hear it from a male and answer Amen. Alternately, many Poskim maintain that women can say it without Shem U'Malchus.

Rav Shlomo Zalmen Auerbach Zatzal maintained that the custom is for women not to say this blessing. (And ruled as such Halacha L'ma'aseh in 1981. See Halichos Shlomo page 33) 

 
One thing is clear though from the Poskim: even if a woman does want to participate in this Mitzvah and it is her custom to do so, she must not do it at the expense of Hilchos Tznius, and thus should be careful to stand at some distance from the assembled men.

(This is a very exhaustive topic and beyond the scope of this forum.  If anyone is interested in exploring this fascinating topic further, here are some starting references:  KafHaChaim 229:8, Shu"t Chasam Sofer Orach Chaim Siman 56,  Shu"t Minchas Yitzchak Vol. 8 Siman 15 and 34, Mogen Avraham beginning of Siman 426,  MaHaram Shik Orach Chaim Siman 90m, Chasam Sofer to Shabbos 21a, Shu"t Kesav Sofer Orach Chaim Siman 34, Shu"t MaHaril Diskin Kunteres Achron Siman 26, Ben Ish Chai Shana Rishona Parshas Eikev Siman 19)

2 )In the event that it is an overcast day and the sun cannot be seen, it is best to wait until a little before midday(Chatzos) and then, if the sun is still not visible, say the Bracha without Hashem's name (Mishna Berura 229:8)

It is best to recite the Birchas HaChama while standing outdoors. (Siddur Ya'avetz). If one is ill or otherwise unable to go outside, the Bracha may be recited indoors, after having seen the sun through an open window.