The Mitzvah of Onah on the Seventh Night after Part of the Night

Is it permissible for a mourner on the seventh night to fulfill the mitzvah of onah after part of the night has passed?

In the Tur, Siman 395, there is a dispute among the poskim whether on the seventh day we say part of the night is like the whole or only during the day we say part of the day is like the whole. The Shulchan Aruch there, Siman 1, rules that only part of the seventh day is like the whole once the comforters leave him. In Pitchei Teshuva, Siman 1, it is brought in the name of the responsa of the Radbaz, Siman 268, that Torah study and marital relations are permitted after part of the night because they contain a bit of mitzvah. However, in Taz, Siman 492, Siman 5, it is proven that even regarding marital relations, we do not say part of the night is like the whole, and therefore one should not be lenient in this. Furthermore, in Sefer Chassidim and also in Prisha in the name of the Maharshal, it is written that even part of the day is not said in this to permit marital relations in a dark house. Practically, from the words of the Shulchan Aruch, it is implied that on the seventh day marital relations are permitted. What is written in cases of great necessity is from the words of the Chayei Adam, who wrote that if the husband needs to travel to another city, etc., it is permissible to be lenient after part of the seventh night, relying on the words of the Radbaz.