In this contribution we propose a segmental duration model for the Galician language. We have focused our work on the study of allophonic durations in their syllabic environment. Firstly, a study of the speech rate over a recorded corpus led us to consider different behaviours in certain types of sentences. Secondly, the corpus was analyzed in order to determine the main factors affecting duration (phonetic class, context, ...). Prosodic factors (stress and final lengthening) were found to be the most determinant, in quantitative terms, to predict timing. Finally, a model for assigning segmental durations is proposed.