The Sages prohibit working on Friday afternoon, informing us that work undertaken then will not be blessed with success. The prohibition goes into effect at Minĥa ketana, which is two and a half (seasonal) hours before sunset (Rashi). There is a more stringent opinion that maintains that the prohibition goes into effect earlier, with the onset of Minĥa gedola, which is one half of a seasonal hour after midday (Maharam). Since this is a rabbinic prohibition, one may rely on the more lenient opinion and work until the later time (SA 251:1; MB ad loc. 3). Even if one has finished all his Shabbat preparations, he may not work during this time, because it is disrespectful toward Shabbat for one to work on something unconnected to Shabbat so close to Shabbat (see Harĥavot).
The Sages specifically forbade regular work during those hours, but permitted ad hoc work. Therefore at this time one may not engage in carpentry, tailoring, electrical work, large gardening projects, computer work, writing a Torah scroll or mezuza, or editing books for pay, because these are all forms of regular work. An expert may, however, do something quick, like set a trap to catch animals, soak dye-producing materials in water, or set a computer to carry out a complex operation, all of which are ad hoc types of work. Similarly, one may water the lawn, clean a room, sew buttons, do the laundry in a machine, or write Torah thoughts by hand or on the computer, as these tasks do not require expertise. One may even do these jobs for pay, though he may not do them for pay every Friday afternoon, even if they involve only unskilled labor, because the combination of the pay and the frequency makes it the equivalent of a regular job (see Rema 251:1; BHL s.v. “igeret”; SSK 42:38-39 and n. 133).
One may engage in regular work, including paid work, on Friday afternoon if it is clear that this work is done in the service of Shabbat. For example, one may give haircuts then because it is obvious to all that people are getting their hair cut in honor of Shabbat. It is permissible for a driver to take people places before Shabbat because this too is considered part of Shabbat preparation. An electrician may perform repairs necessary for Shabbat for pay. However, a tailor may not sew clothing then, even if the clothing will be worn on Shabbat, since it is not apparent that it is being done for Shabbat, as it is possible that the garment is meant for a different time. If, however, he is working for free, he may sew clothing to be worn on Shabbat, whether for himself or for a friend. Accordingly, a non-professional may certainly sew or fix clothing for free in honor of Shabbat (SA 251:2; MB ad loc. 7; BHL s.v. “le-taken”).
There are two additional cases in which the Sages allow people to undertake regular work on Friday afternoon. A poor person who does not have enough money to buy Shabbat necessities may continue to work then (MB 251:5), and anyone may work then in order to avoid damage or loss. Thus, a craftsman may finish his work if there is a possibility that if he does not finish it he will lose customers (BHL 251:2 s.v. “ve-eino”). Similarly, one may do on Friday afternoon everything that one may do on Ĥol Ha-mo’ed (MB ad loc. 5).
According to many authorities, commerce is not included in the prohibition of work, so stores may remain open late on Friday. Nevertheless, stores should be closed at least half an hour before Shabbat begins, in order to leave time to wash and get dressed for Shabbat. Nowadays we are customarily more stringent and close shops a few hours before Shabbat. Only stores that sell Shabbat necessities stay open late (MB 251:1, 4; BHL s.v. “ha-oseh,” “ve-eino”).
Those who are going away for Shabbat must plan their trip so that they will arrive at their destination at least half an hour before the start of Shabbat. This way they will be able to organize things for Shabbat when they arrive. If they are taking a long trip, they must take into account possible delays on the way. R. Mordechai Eliyahu advised allowing for double the normal travel time, so if a trip normally takes two hours, one should leave home four hours before Shabbat.