Can I tie tzitzis onto a talis at night, since many hold that there is no chiyuv tzitzis at night, do we need to tie them at a time of chiyuv
You are bringing up an interesting point. Maybe it should not be permitted to tie tzitzis at night because it isn’t the time for tzizis and maybe it is “taaseh v’lo min hasuiy”, that the mitzvah should be made with a direct action and not making it in an indirect way (by making it kosher through removing a problem). The poskim say that it is not an issue and it is permitted. There are however poskim that say that although it is permitted, there is a preference to making them during the day. See sources.
See Pri Megadim O:CH 18-1 M:Z that it is only Taaseh vlo min haasuiy when one makes the item when it is posul, and then makes it kosher by removing the problem, but not by positively making it kosher. Such as making tzitzis that can’t be worn because they have klayim in them, and making them kosher by removing the klayim. This is an indirect action to make them kosher- or in a way, backing into the mitzvah. In our case however, the tzitzis are kosher but they can’t be worn at night, and when the day comes, they become kosher to wear on their own, without any human action. Therefore it doesn’t apply. Also see Teshuvos V’hanhagos 2-13 from the Chofetz Chaim and Chazon Ish, Yitzchok 9-8(4), Moshe 8-47, Halichos Shlomo 3-23.