Previous studies of duration variation in syllable constituents have yielded results for Polish which are clear outliers in relation to those for other languages. We report on a study of this issue in the context of TTS development, using a large annotated database. Global and local duration distance measures are applied to phoneme and syllable level units, and generalised iambic and trochaic duration patterns are compared with grammatical structure. The study suggests that Polish is more syllable-timed than previously thought, and that there is tendentially a relationship between syllable duration patterns and word sequences.