==When does [[Shabbat]] start?==
# It is absolutely forbidden to do any Melachah (activities forbidden on [[Shabbat]]) after sunset on Friday. (See footnote for background)<ref>
#For men, it is forbidden to do any Melachah once he has begun the second to last paragraph of [[Kabbalat Shabbat]].
* Shulchan Aruch 261:2 writes that one should accept [[shabbat]] early during the time between [[Shekiyah]] (sunset) and [[Bein HaShemashot]] (twilight) to fulfill the mitzvah of Tofeset [[Shabbat]]. Shulchan Aruch explains that this time period is the length of time it takes to walk 3.25 [[mil]]. Then [[Bein HaShemashot]] (twilight) lasts for a period of 3/4 of a [[mil]] which is followed by [[Tzet HaKochavim]] (emergence of the stars). For this discussion, we're assuming that a [[mil]] is considered 18 minutes like the ruling of Shulchan Aruch 459:2 and Mishna Brurah 459:15. If so, Shulchan Aruch holds that one must accept [[Shabbat]] 13.5 minutes before [[Tzet HaKochavim]] which is 58.5 minutes after [[Shekiyah]].
* However, Mishna Brurah 261:23 quotes many Rishonim and the Gra who hold that between Sheiyah and [[Tzet HaKochavim]] there is a short [[Bein HaShemashot]] of 3/4 of a [[mil]] (13.5 minutes) and afterwards it's considered nighttime Deoraitta. According this opinion the Mishna Brurah writes that one may absolutely stop doing Melacha (activities forbidden on [[Shabbat]]) before [[Shekiyah]].