The Shulhan Aruch, in Orah Haim (672), writes that the proper time for lighting the Hanukah candles is the "end of sunset," or Set Ha’kochavim – nightfall (listen to audio recording for precise citation). Practically speaking, this means that one should light the Hanukah candles fifteen minutes after sundown. One should make an effort to light the candles no earlier or later than this time.
If one cannot light the Hanukah candles at the preferred time, he may light them later during the night. The Magen Abraham (Rabbi Abraham Gombiner, Poland, 1637-1683) was of the opinion that a person who returns home late at night lights the Hanukah candles without the Berachot, unless there is somebody else awake in the home who sees the lighting. Otherwise, according to the Magen Abraham, the Berachot are not recited, since there is no Pirsum Ha’nes (publicizing of a miracle) in such a situation. Other authorities, however, including Rav Yaakob Haim Sofer (Baghdad-Israel, 1870-1939) and Rav Shlomo Zalman Auerbach (Israel, 1910-1995), in Shalmeh Mo’ed (p. 218), disagreed. In their view, one may recite the Berachot over the candle lighting even if nobody else witnesses the lighting. This is the view accepted by Hacham Ovadia Yosef. Preferably, however, one should wake up one or two members of his household so they can witness the lighting.
Many people are unable to light the Hanukah candles at the preferred time because of professional obligations, and therefore end up lighting later, when they return home from work. However, people who must light the candles later for work-related reasons must ensure to light at the proper time on Sundays, or other days when they are not at work. Even if somebody must light later at night on workdays, he must make a point of lighting at the proper time whenever this is possible. It should be noted that the practice in most Yeshivot and Kollelim is that the students leave when the time for candle lighting arrives so they can return home and light at the proper time, and they then return to the Yeshiva or Kollel to resume their studies.
One is obligated to place enough oil in the lamp to sustain the flame for at least a half-hour. There is a custom that was famously observed by the Brisker Rav (Rav Yishak Zev Soloveitchik of Brisk, 1889-1960) to add a larger amount of oil to the Hanukah lamps, so that they continue burning late into the night. The Brisker Rav felt that since nowadays there are people walking about outside even until the late hours, it is proper to have the Hanukah candles burn until the late hours of the night to publicize the miracle. However, even he conceded that this is not required according to the strict Halacha, which requires simply providing enough oil for the candles to burn for a half-hour.
It is forbidden to begin eating a "Se’udat Keva" ("established meal") before one lights the Hanukah candles. The prohibition begins a half-hour before the preferred time for lighting (assuming one plans on lighting at the preferred time). Thus, for example, if sundown occurs at 4:30 PM, such that the preferred time for lighting is 4:45, it would be forbidden to begin eating a meal from 4:15. A "Se’udat Keva" for the purposes of this Halacha refers to a quantity of a Kabesa (approx. 2 oz.) or more of bread. It is thus permissible to eat a small snack or have a drink before lighting the Hanukah candles, but it would be forbidden to eat a slice of pizza, for example.
Halacha also forbids studying Torah before lighting the Hanukah candles. This prohibition, however, begins only once the time for candle lighting arrives; one may learn Torah within a half-hour before the time for candle lighting.
Summary: One should endeavor to light the Hanukah candles fifteen minutes after sundown; if this is not possible, one may light later during the night. One must supply enough oil to sustain the flame for a half-hour, though some have the custom to add larger amounts of oil. One should not begin eating a meal within a half-hour before the time for lighting Hanukah candles until he lights, and one should not learn Torah once the time for candle lighting arrives, until he lights.
