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.