Spaced retrieval practice has been repeatedly demonstrated to improve learning, but its implementation is often constrained by real-world time limitations. This study investigated whether, under fixed study durations, learners should prioritize spacing or repetition. Across two experiments (total N = 1589), participants practiced Indonesian vocabulary under four conditions that varied in spacing and repetition. Item difficulty was also manipulated. Results showed that increasing repetitions at the cost of spacing enhanced immediate test performance, particularly for harder items. These findings suggest that spaced retrieval practice is effective only when learners have sufficient prior repetitions to retrieve information successfully. This study highlights the trade-offs between spacing and repetition under time constraints and offers practice insights for optimizing learning strategies.