Metagames are a crucial part of most Magic tournaments, and preparation for a Constructed tournament generally hinges on trying to figure out what the most popular decks will be, and how to beat them. But a Limited metagame is often underexplored and undervalued way of attacking a format, with both the cards that are picked late and the type of decks most people build being legitimate angles of attack quite frequently.
Broadly speaking, the best time to attack a metagame is when it’s largely settled. This means a broad acceptance of what archetypes and pick orders for draft, and a general acceptance of how pools should be built in Sealed.
A common misconception is that metagames are only attackable late in the format, when a lot of people consider it solved, but all you really need to attack a metagame is a common shared understanding of the format. This is often doable as early as the first or second week of a draft format, with there being general assumptions as to what the best commons and uncommons or strategies are. Draft metagames will often go through cycles in players’ understanding of them, with new archetypes being understood and added to the public consciousness of the format, which in turn allows for some other archetype to be understood and exploited before the community in general catches on.
Sealed metagames are a little more complicated in terms of when they can be attacked, as the only get to attack on the axis of having an archetype that lines up well against widely played archetypes, as opposed to getting to use cards that are undervalued by other players and passed to you late in draft as a result. As a result, there needs to either be a fairly established understanding of a format, or a generally used heuristic of Sealed formats that can be exploited for you to be able to effectively metagame in sealed.