  We show that generalizations of classical and quantum dynamics with two times
lead to fundamentally constrained evolution. At the level of classical physics,
Newton's second law is extended and exactly integrated in $1+2$ dimensional
space, leading to effective single-time evolution for any initial condition. In
the domain of quantum mechanics, we follow strictly the hypothesis of
probability conservation by extending the Heisenberg picture to unitary
evolution with two times. As a result, the observability of two temporal axes
is constrained by a generalized uncertainty relation involving level spacings,
total duration of the effect and Planck's constant.
