Before there were clocks and standard time, time was determined in relation to the position of the sun—hence, the importance of the sundial. As a rule our Sages followed this course, teaching, for example, that one may daven mincha until sunset, may recite the morning shema until a quarter of the day has passed, or that the earliest time to do a brit milah is at sunrise.
However, on occasion our rabbis, clearly seeking to impart an additional lesson, used some other reference point. The first Mishna in masechet Brachot (one we will, PG, learn this upcoming Sunday as we begin the 14th cycle of Daf Yomi) teaches that the earliest time to say kriat shema is “at the hour that the kohanim enter to eat their terumah”. While the Mishna could have said that one may recite shema from tzeit hacochavim, the "time the stars come out”, the Mishna wanted to teach that kohanim, having gone to the mikvah as part of the process of becoming tahor, pure, may eat terumah at tzeit hachochavim, despite the fact that they had yet to bring a sacrifice to complete the process of tahara.
When it comes to lighting Chanukah candles, our rabbis used both the natural time of the sun and the social time of the workday. “The mitzvah [of lighting candles] is from sunset ad s'tichleh regel min hashuk, until there are no more feet [people] in the marketplace” (Shabbat 21b). The Gemara suggests two possible meanings for this timeframe. One possibility is that this is the time period in which one may light the candles. But once there "are no feet in the marketplace”, one can no longer fulfil the mitzvah of lighting the candles. As pirsumei nisa, publicizing the miracle, is an integral part of the mitzvah, there is little point in lighting if there is no one in the street to see the candles.
Alternatively, the Gemara suggests that this is the length of time that the candles must stay lit. One need not necessarily light during this specific time period, but whenever one lights, it must last the length of time between these points.
Yet these explanations do not give a specific time for tichleh regel min hashuk. Presumably, this is because the time the market empties varies from place to place, and even from night to night. With the marketplace a meeting place of Jew and non-Jew, we might anachronistically explain that, in years when Chanukah coincided with the days leading up to Christmas, one would have to keep the candles burning longer.
Nonetheless, the Gemara does ask when the time is that the marketplace closes, answering that it is “when the feet [people] of the Tardumai” leave the market. As Rashi explains, the Tardumites were a nation that collected small pieces of wood and remained in the marketplace later than all others. They did so in order to be able to provide wood to those who, upon coming home, realized that they had run out of wood. These people would quickly run out to the marketplace, hoping that the lumber store was open late, lest they have a very cold night.
The Talmud could easily have said the time for lighting candles is “from sunset until the Tardumites leave the market”, skipping the redundant step of ad stichleh regel min hashuk. It could have, but it did not—because the Talmud wanted to teach more than the optimal time to light the candles. The Gemara wants to teach us something about the purpose of lighting candles.
The shuk is a place where the material reigns supreme. It is where we look to make money, to get the best deal possible. It is the place where we focus on the notion, “If I am not for myself, who will be for me?” It is a rough and unforgiving place where those not versed in its ways may fare poorly. None of this is inherently problematic. Jewish law expects those who enter the shuk to have a basic understanding of how it operates, and the marketplace serves many crucial functions necessary for the benefit of society.
However, the Jewish marketplace must look beyond Milton Friedman’s mantra that “the business of business is business”. The marketplace must be a place where one also realizes, “If I am for myself only, what am I?” The marketplace must be a force for good beyond the economic sphere. It is a place where light must shine, where we learn to share our blessings with others. At times, we must remove the regel, the foot, from the marketplace. Sometimes, instead of running to and fro looking for more deals and ways to make more money, we must stop and pause to ensure that we are running to the right place, “to the World to Come” and not to “a pit of desolation”.
Yet we must light before the regel leaves the shuk. The candles must illuminate the marketplace; once all have left, of what influence can even the most powerful light have? The spiritual must operate within the physical. One must not delay—“if not now, when?” It is not by accident that our rabbis ordained we must light the candles outside of the house, or at the very least, by the window. If a light is lit and no one sees it, can we be said to have performed a mitzvah?
Perhaps one of the miracles of Chanukah that we must publicize is that the marketplace can be a place of religious growth. It is the place where more mitzvot of the Torah can be fulfilled than any other. It is the place where those who conduct their masah umatan b’emunah, business faithfully, will be well equipped to answer G-d’s first question upon greeting us in the olam haemet: Nassata venatta bemunah, Were your business dealings conducted faithfully? (Shabbat 31a).
 According to this view, the longer the market remain open, the greater the stringency regarding the lighting of candles. According to the first view, which requires only that one light at some point during this time, longer store hours lead to leniency.
 It is worth noting that the only place where the Mishna discusses the lighting of the menorah (Bava Kamma 6:6) is in regards to a discussion as to the culpability for damages caused by fire in the marketplace. While a store owner must, under normal circumstances, take the blame for a fire caused by putting candles outside his store, our Sages debate whether or not the same holds true when it is the Chanukah candles that one places on the street in the marketplace.
 There are well over 100 mitzvot relating to our monetary possessions, more than any other area of Jewish life.
I would like to express my thanks to Rabbi Dr. Aaron Adler, whose words served as the catalyst for this devar Torah.