Question: Where is the open-air sitting of Tynwald usually held?
Sentence: By ancient custom, an act did not come into force until it had been promulgated at an open-air sitting of Tynwald, usually held on Tynwald Hill at St John's on St John's Day (24 June), but, since the adoption of the Gregorian calendar in 1753, on 5 July (or on the following Monday if 5 July is a Saturday or Sunday).
Answer in sentence: yes