Before the first spin of the session
Each spin lands new symbols on the 6x5 grid, and four or more Scatter longships anywhere on screen start the Free Spins round. How often that happens is not known in advance. The RTP describes an average over a large number of spins, so it does not say when the bonus comes. The result of one session is random and can sit above or below that average.
Every payout on the 6x5 grid is set by the RTP version the game runs. That version is shown only in the game rules. Read those rules before you compare this game with another title, because a figure from a different page may describe a different version.
Each cascade drops new symbols onto the 6x5 grid until no more winning combinations form. The maximum win is a ceiling, not an expected result, and it is reached very rarely. A large cascade chain can still end well short of that top figure, so the ceiling says little about a typical session.