Supply and demand suggest that, laws permitting, the new time per day would be split, some of it going to the workplace and the rest not. That would be entirely

Supply and demand suggest that, laws permitting, the new time per day would be split, some of it going to the workplace and the rest not. That would be entirely due to a labor supply shift, i.e a rise in workwrs' willingness to provide hours. If supply somehow did not rise, there would be no change in hours worked, as employers' demand for labor (which is equivalent to the money they expect to earn by employing someone for another hour) would be unchanged by the new tech.