# Many Rishonim hold that it is rabbinically forbidden to tie a knot which is either professional or meant to last for more than 24 hours. Some Sephardim hold that a non-professional knot is only rabbinically forbidden if it meant to last a week. Some Rishonim hold that a knot which is permanent even if it's not professional is Biblical prohibited.<Ref>
* According to Rashi, (Gemara Shabbat 112a), tying a knot that lasts forever is forbidden Deoritta, tying a knot that is untied after some time is forbidden Derabbanan, and tying a knot that is untied all the time is permitted. (For a precise explanation of Rashi see Bet Yosef 317:1 and Taz 317:1.) The Rosh 15:1 agrees. The Rif 41b, however, explains that a professional knot which is meant to last forever is forbidden Deoritta, a non-professional knot which is meant to last is forbidden Derabbanan, and a non-professional knot which is not meant to last is permitted. The Rambam 10:2 adds that a professional knot which is not meant to last is forbidden Derabbanan. S”A 317:1 and Yalkut Yosef 317:1-4 rule like the Rif, while the Rama and Mishna Brurah 317:5 and 14 are concerned both for Rashi and the Rif. Pri Megadim M”Z 317:3 and Mishna Brurah 317:5 writes that according to the Rambam even if it lasts a long time it’s permitted as long as it is not meant to last forever.
* The Bet Yosef 317:1 explains based on the Tur that a knot that lasts for less than a week is considered to be untied every day. Yalkut Yosef (vol 2 p. 555) agrees. Rama 317:1, however, quotes the Maharam MiRotenburg’s who says that a knot that lasts for more than a day is forbidden. Pri Megadim (E”A 317:2) and Mishna Brurah 317:6 clarify that one day means 24 hours. Sh”t
Yabea Omer 8:39:8 agrees that one day means 24 hours for this halacha, unlike the Tal Orot who says that it goes by the halachic day. Taz 317:1, Eliyah Rabba 317:2 Aruch HaShulchan 317:8, and Kaf HaChaim 317:14 rule like the Maharam. </ref>
# A knot which is both non-professional and meant to be undone within 24 hours may be tied. <Ref> The Rama 317:1 quoting Tur and Mordechai; Mishna Brurah (317:6) explains it as anything less than 24 hours. </ref> Some Sephardic authorities permit a non-professional knot which is meant to last less than 7 days. <Ref> Rama also quotes Kol Bo and Hagahot Maymoniyot. Chazon Ovadia Shabbat Part 5 page 47 and Yalkut Yosef (317:6) writes that Sephardim hold like this opinion. </ref>