The structure of the equations of motion of a time-dependent mechanicalsystem,subject to time-dependent non-holonomic constraints, is investigated intheLagrangian as well as in the Hamiltonian setting. The treatment applies tosystemswith general nonlinear constraints, and the ambient space in which theconstraintsubmanifold is embedded is equipped with a cosymplectic structure.In analogy with the autonomous case, it is shown that one can define analmost-Poisson structure on the constraint submanifold, which plays aprominent rolein the description of non-holonomic dynamics. Moreover, it is seen thatthecorresponding almost-Poisson bracket can also be interpreted as aDirac-type bracket.Systems with a Lagrangian of mechanical type and affine non-holonomicconstraintsare treated as a special case and two examples are discussed.