The effect of planning on second language (L2) learners' oral performance is a hotly debated topic in the field of second language acquisition. However, studies on the effect of different amounts of planning time have been quite limited, especially in a testing context. The present study investigated the effects of different lengths of pretask planning time (nil, 30 seconds, 1 minute, 2 minutes, 3 minutes, and 5 minutes) on L2 learners' oral test performance in terms of both the quantity and quality of the test-takers' linguistic output using discourse analytical measures. The findings suggest that the provision of planning time positively influenced both the quantity and quality of oral production; of the three aspects of quality (fluency, accuracy, and complexity), accuracy improved the most, with 1-minute planning time being the threshold that led to significant improvement. Concerning different planning lengths, a positive effect of planning was not always observed in line with the increase of time: too short a time (e.g., 30 seconds) was inadequate for improvement, whereas too long a time (e.g., 5 minutes) engendered a diminishing effect.