Signs can be divided to syllables and further into transitions and nuclei based on the signing flow of the handshapes. Here, a mixed effects linear regression model is used to describe the variation in the duration of the syllable nuclei in a data set of 341 signs (474 syllables) produced by five native FinSL signers during a map task. The phonetic fixed variables are the duration of the adjacent transients and syllable nuclei; phonological fixed variables are the syllabic length of the sign, the syllable position within the sign, and the sign type (functional or content bearing). Both preceding and following nucleus had a significant effect on the nucleus duration, while an asymmetric effect was found for the transitions: only the postnuclear transition had a significant effect. The syllable structure had no effect. However, the nuclei were shorter in function signs. These results suggest that signs are produced in two stages where the first stage, preparatory transition, is merged with the production of the previous syllable, and the second stage consists of executing the sign.