sechel: One source is today’s rambam hilchos tefillah see the ראבד
All of a sudden we ignore Rav Shulchan Aruch who writes clearly that one has to daven lechatchilah before zeman tefillah, and bedieved before chatzos?! Since when does a statement in the Rambam (and I don’t even know what you’re referring to) override the Baal Hatanya?
See also צמח צדק הלכות ציצית about if women can make a bracha on a mitzvah they are not obligated (it’s a long teshuvah and talks about making brachos if one is not obligated)
Totally irrelevant. Not being obligated in a mitzva does not make it a berachah levatalah. Davening after chatzos does. Check it out.
Btw, yb, why davka Shabbos afternoon? In 770 there are people who daven long long after chatzos even during weekdays.