This study investigated the optimal feedback intervals for tasks of varying difficulty levels in online testing and whether task difficulty moderates the effect of feedback intervals on student performance. A pre-experimental study with 36 students was conducted to determine the delayed time for providing feedback based on student behavioral data. A formal experiment with 80 students was then conducted to explore the joint effects of feedback interventions and task difficulty on student performance improvement. The findings revealed that feedback conditions had no significant impact on student learning gains in easy or difficult tasks. However, for medium difficulty tasks, feedback delays of 23 and 30 s led to greater academic improvement compared to immediate feedback, while feedback with a 35-s delay resulted in worse performance. Overall, the study highlights the importance of considering task difficulty when determining optimal feedback intervals and suggests that well-timed feedback can significantly enhance student learning, especially for tasks of moderate complexity. This challenges the common practice of providing immediate feedback, which may not always be optimal. Moreover, the findings of this study provide valuable insights for educators and instructional designers when designing online assessments and feedback mechanisms.