In polymeric liquids undergoing cross-linking reactions, rheological properties continuously change as a function of time. Consequently, the materials do not obey the time translational invariance and therefore the principles of linear viscoelasticity. In this work, we propose a methodology in which principles of linear viscoelasticity are transformed from the real time domain to the effective time domain. In the latter, the readjustment of the material clock, which accounts for the time dependency, facilitates validation of the effective time translational invariance. By carrying out experiments on cross-linking PDMS, we show that material that is undergoing time evolution in the real time domain indeed validates the Boltzmann superposition principle and convolution relation relating creep compliance and relaxation modulus in the effective time domain.