[slavik81]

Not every unit of a resource has the same value. Marginal utility is typically a curve, with the value of each unit of the resource decreasing as you have more of it.

In theory, yes, the time someone spends working is worth less to them than what they are paid. Hence why they spend it working.

But, in theory, they only stop working because the remaining time they have left in the day is at that point worth more to them than their hourly pay.