Femtosecond hyper-Rayleigh scattering has recently been used to determine the spatial correlation length between nonlinear optical chromophores in polymer films [G. Olbrechts et al., Chem. Phys. Lett. 253, 135 (1996)]. This correlation length corresponds to the effective interaction length for frequency doubling in waveguide format, as derived from phase-matching curves. The temporal characteristics of this correlation length have now been studied and compared with thermal relaxation times, obtained with coherent second-harmonic generation. The correlation length decays much faster than the second-harmonic intensity, indicating that the efficiency of a second-order waveguide process could decay much faster than generally anticipated. (C) 1996 American Institute of Physics.