Performing long-time thermal equilibrium measurements of spectral diffusion broadening of photochemical holes, we recently established an algebraic time dependence of the dynamics of two-level system (TLS), which we interpret in terms of TLS-TLS coupling (Phys. Rev. Lett. 76 (1996) 2085). For this purpose we utilized the continuous cooling property of our He-3/He-4 cryostat. To extend the accessible temperature range we have constructed a cryostat which allows optical experiments lasting several weeks at temperatures of 1.5K and above. Here we report data obtained at 2.0K in a time range from 10 s to 10(6) s. Interpreted in the framework mentioned above, the results indicate the onset of a thermally induced break-up of the TLS-TLS coupling.