We implement two theories about the temporal organization of speech in an optimization-based model of speech timing and conduct simulation experiments in order to test whether both theories can account for the phenomenon of foot-level shortening (FLS) observed in English speech corpora. Results suggest that a model that induces compensatory timing relations between syllables and feet predicts empirical results very accurately. However, we also observe that the FLS effect can equally well be explained under the assumption that suprasegmental timing is confined to localized lengthening effects at the heads and edges of prosodic domains. Implications for theories of speech timing are discussed.