The Ulysses Jupiter encounter will include the first spacecraft pass through the dusk magnetosphere and will allow new tests of Jovian convection and corotation models. The Cheng and Krimigis [1989> model is extended to suggest that corotation lag occurs principally within the magnetodisk proper, which extends out to ~60--70 Rj. It is predicted that outside this radius, in the pre-midnight sector, spin-up to near corotation may occur owing to a local reduction in the outward mass transport rate. The mass loss may occur mainly in the dawn sector, to the magnetosphere wind and the dawn magnetosheath.