Q. Can you light in a shul (the menorah) before the shkiah (sunset)?
A. Shulchan Aruch (O.H. 672: 1) rules that "you do not light the menorah before the shkiah – and one opinion is that in need you may light after plag hamincha" [one and a quarter hour (zmaniyos) before nightfall]. Mishna Berura (ibid. 3) adds that you can light with a brocho.
Nonetheless Shevet Halevy (4: 66) advises that it is better to light using an agent and on the right time rather than lighting oneself before the shkiah (after plag). A few Poiskim also maintain that you should avoid kindling before the shkia and if you have too you should not recite a brocho (Piskey Teshuvos ibid.Nitey Gavriel, Chanukah 3: 11).
However in shul, where one of the main reasons for lightning is persumei nisso or publicizing the miracle and the people are present there and can see the lights, you may be more lenient when it is difficult to gather them at a different time (Shov Yaakov 22, Zivchei Tzedek Hachadoshos p. 211, see also Mishna Berurah 671: 46)
Horav Shlomo Miller's Shlit'a opinion is in general to avoid kindling before shkiah unless it is utterly necessary, such as Erev Shabbos were we do recite a brocho. Nonetheless, in a shul, you can be more lenient.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a