  We study several issues related to the different choices of time available
for the classical and quantum treatment of linearly polarized cylindrical
gravitational waves. We pay especial attention to the time evolution of
creation and annihilation operators and the definition of Fock spaces for the
different choices of time involved. We discuss also the issue of microcausality
and the use of field commutators to extract information about the causal
properties of quantum spacetime.
