The CEO doesn't stop being paid when she walks to the bathroom, and a cashier doesn't stop being paid when he's waiting for a customer to show up. wpietri is talking about a shift in the granularity of trading your labor for money, so that you aren't paid for a day or an hour of work, but for the exact number of minutes you performed useful work.
The shift is away from paying an employee for 8 hours of work--knowing that he will only be performing useful work for some fraction of that time--towards paying the same employee only for the time spent being productive.
Since most people aren't able to work productively for an entire 8 hour shift, this change probably means a net decrease in wages.
We've already started to see this with computer scheduling in retail. Assigning split shifts, irregular shifts, and scheduling the bare minimum number of employees required to minimize employee downtime.
As somebody who was a self-employed consultant for years, I get that being one's own boss has upsides. But I always maintained a large buffer of cash and could price in all the time I spent looking for work. Things like Uber and the new retail scheduling trend don't allow for that, and as far as I'm concerned amount to calculated exploitation of desperate people.
In some sense, that's nothing new in labor history; we've always had exploitation of desperate people. But that's no excuse for increasing it, and in particular I despise Uber's "we're just helping people be independent entrepreneurs" spin to cover up that exploitation, especially when their whole plan is to kick those supposed entrepreneurs out into the snow the moment they have self-driving cars.