This is remarkably garbled writing. No surprise that the writer is a professional philosopher. The structure of the sentence suggests a comparison between two magnitudes measured in the same way, so when one reads "difference" and "time spent by a worker", one expects a comparison again measuring something in terms of how long it takes. Value in Marx is indeed closely related to that, but why would somebody reading this text as an intro to Marx know that?
The word value has many meanings. In the writing of Marx, when value is mentioned without any qualifiers, it usually refers to how long it takes to produce something. And the focus is almost never anecdotal, so when Marx says a capitalist does this, a worker does that, this or that product takes this or that amount of work, it's almost always not really about a particular person, but about what happens usually, what happens on average.
A commodity has direct use value, which are not abstract happiness points like what somebody who has only studied neoclassical economics might think, but a plain description of what the commodity is useful for due to its known physical properties. And a commodity has exchange value, the exchange ratios with other commodities, which strongly correlates with value (in Capital volume 3 this is modified due to a tendency of profit rate equalization between sectors with low and high capital intensity).
Commodities are bought for their use value. Commodities usually sell at value (roughly). Marx says it's not different with workers. So their payment has to do with what it takes to keep them alive. Their use value is their ability to work.
I have the entire Marx-Engels Werke in German. Would you mind giving an actually usable reference?
