The timeline says that the Merethic Era began ME 2500 with building the Adamantine Tower, but how is that possible if the Convention (guess this is a proper name, hence the capital letter), where the Aedra (minus Magnus and the Magna Ge) decided that Lorkhan must be punished, took place there? Even the wiki about the Convention says right at the top that it occured during the dawn era.
Really doesn't make sense to me... did I miss something or did I just find a mistake in the Fandom Wiki?
It’s more of a mistake with the wiki. The Merethic era has no dates just approximations so saying that the Merethic era began with a specific event and a date isn’t necessarily possible. And even if it did have dates, it wouldn’t begin with 2500 it would start at 0. But it is generally accepted that the Adamantine tower was constructed prior to the punishment of Lorkhan due to that being the location of the debate and later Auri-El shot his heart into the sea.