This study investigated how Mandarin speakers use duration to mark contextual factors, namely epistemic bias, evidential bias, and the presence of antecedent, in their production of Mandarin positive polar questions, ending with either the particle -ba (PPQ-ba), -ma (PPQ-ma), or a prosodic pitch rise (PPQ-H%). Thirty native Mandarin speakers participated in a discourse completion task, producing sentences with a Subject-Verb-Object structure in response to different discourse scenarios. We designed 14 conditions, each encompassing four discourse prompts, to elicit sentences with all felicitous combinations of the contextual factors. Syllable duration was analyzed. Our findings revealed that contextual factors significantly influenced the syllable duration of PPQ-ba sentences but not that of PPQ-ma or PPQ-H% utterances. In PPQ-ba, the lengthening was localized to the verb in stimuli with negative evidence or a negative antecedent. We conclude that Mandarin speakers utilize duration to mark pragmatic functions in PPQs, but only to a limited extent, suggesting that duration is unlikely to be the primary prosodic cue in PPQ production.