When the rancher spends that 8 hours producing potatoes, she spends 8 hours less producing meat...
Is this usage of less correct, or should fewer be used instead?
When the rancher spends that 8 hours producing potatoes, she spends 8 hours less producing meat...
Is this usage of less correct, or should fewer be used instead?
See: "Less" vs. "fewer"
The relation between less and fewer is fairly complex. In non-count singulars only less is possible: Kim has less/fewer money than Pat. In plural NPs we have:
[17]
i. She left less than ten minutes ago.
[...]Both [i] and [ii] have than + numeral. In [i] ten minutes expresses an amount of time rather than a number of individuated units, and in such cases fewer is virtually impossible—just as few would be in a comparison of equality: She left as little/*few as ten minutes ago. Similarly with We paid less than thirty dollars for it; She’s less than forty years old; We were going at less than ten miles an hour.
"Less than ten minutes" implies "eight hours less" is the more correct choice.
According to Strunk and White (Mcmillan, 1979, page 51):
Less. Should not be confused with fewer.
Left-hand column: He had less men than in the previous campaign. [incorrect]
Right-hand column: He had fewer men than in the previous campaign. [correct]
Less refers to quantity, fewer to number. "His troubles are less than mine" means "His troubles are not so great as mine." "His troubles are fewer than mine, means "His troubles are not so numerous as mine."
The OP's question concerns quantity not number (compare quantity of time to number of time), so the example should read:
When the rancher spends that 8 hours producing potatoes, she spends 8 hours less (not fewer) producing meat...