Q. Should one accept in advance the fast of Erev Rosh Hashana and until when should one fast? Does one have to fast if it was not the tradition of his parents but he davens in a minyan where people fast?

A. Shulchan Aruch (O.H. 581: 2) mentions that there is a Minhag or tradition to fast on Erev Rosh Hashanah.

Mishna Berura (ibid 16) rules that this fast does not require acceptance before or the fasting more than after ‘Chatzos’ or midday.
In our days, it is customary in many congregations to do a ‘Siyum’ or finish a Talmudical tractate and avoid the fasting.

Rabbi A. Bartfeld as revised by, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a