n. Time that an employee takes off work to perform non-work-related tasks; the salary or wages earned while performing such tasks.
It may be the worst-kept secret in the workplace: People are working more undertime — stealing time off during the day to compensate for heavier workloads and more stress. Undertime can take many forms, from hours spent away from the office on errands or shopping to chunks of time spent at your desk surfing the Internet.
—Sue Shellenbarger, “Why You Can Hit the Gym — but Not Get a Manicure — on Company Time,” The Wall Street Journal, April 18, 2002
1983 (earliest)
Taking overtime into account, for example, shows that productivity in manufacturing (measured by output per worker-hour) increased by 4.7% a year between 1980 and 1983, only a little less than the 4.9% of the unadjusted measure. But officially-recorded overtime ignores changes in "undertime" — hours paid-for but not worked.
—“Productivity: will the growth last?,” The Economist, May 15, 1983