I'm guessing early May is the HOME release. They've given us the fan favourite starters (Charizard, Cinderace, Greninja) and the OG forms of the Hisui starters (Who were all given tera types that their Hisui counterparts are strong against) which is just a nice nod to Legends, I guess.
Of course there's Delphox, Chesnaught, Inteleon and Rillaboom left, but I doubt they would bother giving them their own raids. The Gen 8 starters are in the game so they always make most starters available in the generation after (Just how Gen 7 starters were in the data for SWSH) and the only logical reason I have for Gen 6 is that it would be weird to include Greninja but not the others outright (I'm instantly contradicted by Gen 5, kinda, so at this point, I genuinely dunno) I'm also guessing they wanted us to do these super hard raids using everything we catch/theorise from SV, whereas after HOME raids can be done using transfers incl legends.
Either way, I think they are done with the pre-HOME raids with the conclusion of Iron Leaves/Walking Wake again and the fact that the Blissey raids are running again in tandem with the final raid.
The above probably means nothing and I'm just clutching, but given that the new raids end on the 1st May is an indication, I'm betting on it being that first week otherwise they've sailed by their Early 2023 / early Spring window regardless of how you look at it.