Translation:Shulchan Aruch/Orach Chaim/18
18: The Time for Tzitzit.
1 Night is not the time for tzitzit because it was reduced from "and you shall see it". According to Maimonides, anything that he wears at night is exempt, even if it is designated for the day, and what he wears during the day requires, even if it is designated for the night. And according to Rabbi Asher, a garment that is designated for the night is exempt, even if he wears it during the day, and a garment that is designated for the day – or for the day and night – requires, even if he wears it during the night. Gloss: And a doubt concerning blessings is to be treated leniently; therefore, one should not bless upon it unless he puts it on during the day and it is also designated for the day [Haggahot Maimuni]. And after the Evening Prayer, even though it is still daytime, one should not bless upon it [Decisions of Rabbi Israel Isserlein, Chapter 121]. And at the night of Yom Kippur, one should wrap himself when it is still daytime, and bless upon it [Tashbetz].
2 Sheets – even though a man sleeps in them in the morning – tzitzit are not attached to them.
3 From when does one bless upon the tzitzit in the morning? From when one can differentiate between its blue threads and its white ones. And if he puts it on from the rise of dawn and onward, there are those who say that he blesses upon it, and so is the custom [Mordecai, Chapter 2 of Megillah]. And if he put in on before that, for example at Selichot, he should not bless upon it, and when the day will illuminate, he should tap it and bless [Tashbetz].