  Rovelli's `` quantum mechanics without time'' motivates an intrinsically
time-slicing independent picture of reduced phase space quantum gravity, which
may be described as ``quantization after evolution''. Sufficient criteria for
carrying out quantization after evolution are developed in terms of a general
concept of the classical limit of quantum mechanics. If these criteria are
satisfied then it is possible to have consistent unitary evolution of
operators, with respect to an infinite parameter family of time-slicings (and
probably all time-slicings), with the correct classical limit. The criteria are
particularly amenable to study in (2+1)-dimensional gravity, where the reduced
phase space is finite dimensional.
