Shulchan Arukh Orach Chayim · Siman 18

English

The Time of ציצית. Containing 3 Se'ifim: Night is not the time of tsitsit , because [the obligation is] limited by [the verse] "and you shall see it" (Numbers 15:39). According to the Rambam, anything that is worn at night is exempt, even if it is designated for daytime use, and that which is worn in the day is required [to have ציצית], even if it is designated for nighttime use. And according to the Rosh, a garment which is designated for nighttime is exempt, even if it is worn in the day, and a garment designated for daytime, or both day and nighttime, is required [to have ציצית] even if it is worn at night. Rem"a: And a doubt regarding blessings is ruled leniently - therefore one shouldn't make a blessing on it unless it is worn in the daytime and it is designated for daytime (Hagahot Maimoni). And after the evening prayers, even if it is still day, one shouldn't say the blessing on it (Piskei Mahar"i, 121). And on the night of Yom Kippur one should put on the garment while it is still day and say the blessing on it (Tashbetz).

English

Bedsheets/Blankets, even though one sleeps in them in the morning, we do not affix ציצית to them.

English

From when does one bless on the ציצית [that he puts on] in the morning? From the time when [there's enough light that] one can tell the difference between the techeilet (blue) in it and the white in it. And if he puts it on starting at dawn, some say he makes a blessing, and this is our practice (Mordechi - chapter 2 of Tractate Megillah). And if he put it on earlier than that, such as during [the time of year when we recite] selichot , he should not make a blessing over it [right away], and [then] when it becomes light he should touch [the ציצית] and makes the blessing (Tashbe"tz).