  Kinetics of the optical and Raman response in YBa_2Cu_3O_{6.4} were studied
during room temperature annealing following heat treatment. The superconducting
T_c, dc resistivity, and low-energy optical conductivity recover slowly,
implying a long relaxation time for the carrier density. Short relaxation times
are observed for the B_{1g} Raman scattering -- magnetic, continuum, and phonon
-- and the charge transfer band. Monte Carlo simulations suggest that these two
relaxation rates are related to two length scales corresponding to local oxygen
ordering (fast) and long chain and twin formation (slow).
