(1) Individual independent restaurants aren’t effected by this, it applies to large fast food chains.(“large chains” is embedded in how the bill defines “fast food”, even though its not part of the usual definition of the term.)
(2) They’d have to go back in time to do it (even if they did when the governor signed the bill), since the cut-off date was in the past when the bill was signed. If they were really pro-active, I guess a chain could have bought bread machines and changed its menu in the four days between the final bill text being presented in the committee and the cut-off date, but my guess is none did.
(3) The main thing this bill does is create a uniform state wide regulatory body for fast food (large chain) working conditions including any potential higher-than-general minimum wage, exempting them potential local regulations doing similar things, possibly inconsistently, throughout the state. Wiggling out of the coverage of this bill would wiggle them back into that kind of potential multi-jurisdiction regulation issue; the $20 minimum wage is an initial wage boost for the industry included in the bill before the council is up and running, but not the main focus.