In this recent presentation
Housemarque's Art Director Simone Silvestri says that he had to rush a presentation just after he joined the company as they were about to hit full production.
He joined in March 2024, a few months after Returnal's director left. Full production seems to have started around May-June 2024.
He shows the actual presentation he gave to the team and it's clear that the game was extremely early, with a lot of basic concepts still being discussed.
Saros was made in less than 2 years of full production, which is much faster than your average modern game.
Would love to know what the original Returnal director was working on.