Linking one's contribution to those of others' is a salient feature demonstrating interactional competence in paired/group speaking assessments. While such responses are to be constructed spontaneously while engaging in real-time interaction, the amount and nature of pre-task preparation in paired/group speaking assessments may have an influence on how such an ability (or lack thereof) could manifest in learners' interactional performance. Little previous research has examined the effect of planning time on interactional aspects of paired/group speaking task performance. Within the context of school-based assessment in Hong Kong, this paper analyzes the discourse of two group interactions performed by the same four student-candidates under two conditions: (a) with extended planning time (4-5 hours), and (b) without extended planning time (10 minutes), with the aim of exploring any differences in student-candidates' performance of interactional competence in this assessment task. The analysis provides qualitative discourse evidence that extended planning time may impede the assessment task's capacity to discriminate between stronger and weaker candidates' ability to spontaneously produce responses contingent on previous speaker contribution. Implications for the implementation of preparation time for the group interaction task are discussed.