Shalom
Q. I have a chavrusa every Thursday evening at 5:30 PM.
Next week, is it better to cancel the chavrusa in order to light the menorah at the ideal zman? Rescheduling isn’t possible.
Thank you

A. As you are aware Poskim maintain different opinions as to what is the correct time for lighting the menorah. Shulchan Aruch (O.H. 672: 1) and Tur (ibid.) rule that the right time is after the stars appear, at the end of the shekiah. Other opine that the proper time is at the beginning of the shekiah (Biur Halacha Ibid.,Mor U’ketziah ibid., Sidur Sheloh et. al.) Different times such as; 10, 15, 18, 20, 25 minutes after the shekiah are mentioned by various Poskim (see Nitey Gavriel – Chanuka 3: 2.)
Horav Shlomo Miller’s Shlit’a opinion is that on this year’s Chanuka, when the shekiah is around 4.41 pm, you can correctly light at 5.00 pm, and then tend to your shiur.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a