Today’s workforce is often faced with high levels of time pressure. According to the challenge-hindrance stressor framework, high levels of time pressure should have an ambivalent relationship with task performance because time pressure increases both motivation and strain. To investigate these ambivalent relationships of time pressure in daily working life, we conducted a diary study over 5 workdays with measurements taken after work. Eighty-one participants provided data on a total of 294 workdays that were analyzed using Bayesian multilevel structural equation modeling techniques. Results revealed that time pressure had a significant total relationship with task performance on the person level, but not on the day level. Furthermore, our data showed that time pressure was positively related to indicators of strain-related and motivational processes, both at the person level and at the day level. However, multilevel mediation analyses also showed for both levels that time pressure was indirectly related to task performance only via motivational processes, but not via strain-related processes. Our results suggest that between-person relationships of job stressors with work outcomes can differ from the corresponding within-person relationships. Thus, we recommend that future research investigates both motivational as well as strain-related processes for other job stressors not only on the person level but also on the day level. Finally, given the ambivalent nature of time pressure, we also recommend that practitioners keep relationships with both motivation and strain in mind when evaluating and redesigning work environments.