Context: Compressed work schedules, such as the 4-day work-week, have gained attention due to reported benefits like increased productivity and reduced absenteeism. However, findings on stress-related outcomes remain mixed. Problem: Despite growing interest in compressed work schedules, there is limited empirical evidence on how such models affect stress, performance, and team dynamics in software development settings—especially under partial workload compression, as in the 4+ work-week. Objective: This study explores the effects of this compressed work schedule on software development teams, focusing on perceived performance, team-level benefits, and stress levels. Method: We applied an action research approach in two German organizations and took three software development teams under study. Data collection was conducted in a mixed-method approach combining both questionnaires, field-observations and semi-structured interviews. Results: We found that the teams’ performance did not decrease. Related to the perceived stress of the team members, the results differ from team to team. In teams with no reduced workload, the stress-level increased over time. The teams under study valued the Plus-Day concept and used the time for process improvements, source code refactoring, or team development workshops and events. Conclusion: Our results emphasize the importance of change preparation, fostering team autonomy, and the willingness for organizational learning when transforming to a compressed work schedule. The benefits of a compressed work schedule are obvious: higher job satisfaction and increased motivation of the employees.