We've had technological progress that rapidly shifts the number of person-hours per <output> for generations. We don't have to guess. We've seen this play out many times already.

At first, we spend our time one way (say eight hours, just to pick a number). Then we get the tools to do all of that in six hours. Then when job seeking and hiring, we get one worker willing to work six hours and another willing to work eight, so the eight-hour worker gets the job, all else equal. Labor is a marketplace, so we work as much as we're willing to in aggregate, which is roughly constant over time, so efficiency will never free up individuals' time.

In the context of TFA, it means we just shift our time to "harder" work (in the sense of work that AI can't do yet).