Tribunals: Rhine - "begins on the eve of the 1st of May (Walpurgis Night)" (GOTF p. 24) Novgorod - can't find it. Stonehenge - held one year later than everybody else's since 1201 (HtM pp. 24, 116) Loch Leglean - doesn't say (LotN p. 34) Rome - doesn't say (Rome p.60) Iberian - can't find it. Levant - doesn't say (B&S p. 100) Provence - doesn't (Midsummer Night's Dream, p. 16), can't find anything in Mistridge, I don't have the 3rd ed. Covenants.
Grand Tribunals - I assume it supercedes the Rhine Tribunal Tremere Decennials - can't find it. The Gatherings of Twelve Years - "begins on the night of the full moon closest to the summer solstice" (HoH:MC p. 16) The [Verditius] Contests - "begins on Midsummer Eve" (HoH:MC p. 116)