Does anyone today follow Rabbineu Tam time for the beginning of Shabbos? Reading some tshuvas (e.g. Eretz haTzvi) it is clear this was widespread in Europe.
If one has previously been accustomed to accept Shabbos according to the Gra/Baal HaTanya, can one switch to Rabbeinu Tam?
(In particular, if one is sure his ancestors did so in Europe, can one revive this minhag after it fell into disuse after migrating to America?)