Objectives This study aimed at opening up the black box of overtime work among university faculty members by providing information on (i) when faculty members work overtime, (ii) what activities are undertaken during overtime, and (iii) how overtime is experienced.

Methods Data were collected among 120 Dutch faculty members who completed a general questionnaire (addressing general overtime hours, work characteristics, and well-being) and a 9-day diary study (with information on daily overtime hours, activities, and experiences). Analyses of variance were used to analyze the data.

Results Overtime was very prevalent among faculty members, high overtime workers being nonfatigued, engaged employees with positive work characteristics. Overtime was unevenly distributed over the week, being common on Sunday and Monday and uncommon on Friday and Saturday. Overtime activities during the weekend differed from those during the workweek, relatively much time being spent on research during weekend overtime. Overtime activities were experienced differently than activities during regular hours, overtime work being experienced as less effortful and less stressful than regular workhours and weekend overtime being less pleasurable than regular hours and evening overtime.

Conclusions This detailed day-to-day mapping and evaluation of overtime work contributes to a better understanding of overtime work by demonstrating meaningful patterns of overtime over the (work)week and meaningful associations between overtime activities and time-contingent experiences. It is suggested that worktime control plays an important role in explaining the results.

Key terms black box; diary study; overtime work; university faculty member; well-being; workhours; worktime control