“Remember that time is money. He that can earn ten shillings a day by his labour, and goes abroad, or sits idle one half of that day, though he spends but sixpence during his diversion or idleness, ought not to reckon that the only expence; he has really spent, or rather thrown away, five shillings besides” (Benjamin Franklin, 1793).

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Salience of the opportunity cost attached to inefficient use of time depends on how pay is structured.  Studies show when pay is explicitly calculated in relation to units of time (e.g., hourly pay and billable hours) people tend to become economic evaluators of time: Decisions over how to use time becomes driven by economic criteria rather than non-monetary factors such as personal satisfaction and relational concerns. 

This may be a plus when it comes to short-term productivity.  However, Mr. Franklin did not consider the long-term effects for well-being and sustainability of productivity.  A performance-regeneration paradox exists: Time and energy that we invest into work is time and energy that cannot be invested in regeneration.  People that equate time as money are more likely to forgo leisure hours when faced with this paradoxical choice.   
   

For example, a large healthcare management company inadvertently makes the economic cost of time off salient by allowing employees to opt out of the benefit package (including the paid-time-off benefit) in exchange for a higher hourly rate.  In theory, this gives hourly workers flexibility to pay themselves for time off as they choose.  In practice, one new hire described it as no time off unless he could afford to have his pay shorted. 

Perhaps hard-and-fast economic evaluators of time, like Mr. Franklin, can justify idleness by knowing that the productivity of consultants in one recent study was found to increase when the hard workers were required to take regular time off.