Unstructured jobs confront employees with new demands such as determining how, with whom, and with what level of effort job tasks should be executed. Until now, it remains unclear whether these demands yield both straining and motivating effects on employees and therefore constitute challenge demands. To investigate this, we utilized the concepts of job design demands (JDD) and cognitive demands of flexible work (CODE). We focus on planning, effort regulation, development, and coordination, demands. Drawing from the challenge-hindrance framework and self-regulatory assumptions in job demands-resources theory, we hypothesized that adaptive regulation (job crafting) would mediate the motivational pathway, while maladaptive regulation (extended working hours) would mediate the strain pathway. Employing a three-wave lagged design with a four-week interval (n = 129), we conducted path analyses while accounting for autoregressive effects. Contrary to expectations, work engagement was not significantly predicted by CODE/JDD. Exhaustion was positively predicted only by demands to regulate effort, and unexpectedly negatively predicted by planning demands. Extended working hours were solely predicted by development demands. No significant relationships were found between job crafting and CODE/JDD, and no expected mediating effects observed. Further research is needed to investigate boundary conditions that could enhance (un)favorable CODE/JDD outcomes.