I think it'd have to be more than a year if you really want to escape taxation. If you leave the state, earn $7M, then move back a year later, California is going to be taking a close look at when you actually earned that money.

Though moving is easier and cheaper for a single person living in an apartment than someone with a family and house.

If it's legit, why does it matter? Presumably that person's song took off and they were able to forecast that they'd make $X, which was worth the move to WA.

If he's moving to escape taxation, it's not legit (in the eyes of the Franchise Tax Board), and if he did the work while he was living in California, they're going to want (and almost certainly will get) their share.