The quality of epoxy composites reinforced by glass fibers and manufactured by compression molding is affected by the pressurization time. Traditional methods, including differential scanning calorimetry and dynamic thermomechanical analysis, cannot be reliably used to predict pressurization time in the scenario of continuous production and inconstant circumstances seen in industry. In this paper, the rheological behaviors of epoxy under constant temperature were investigated and analyzed to verify if the time–temperature superposition (TTS) principle, which defines the relation between time and temperature in the deformation and relaxation response of a viscoelastic material, could be suitably applied to describe them. The results show that the TTS principle could indeed be used to predict resin viscosity by the horizontal shift factor. A new method based on the TTS principle and written into a program to forecast pressurization time in compression molding is proposed. The uniform surface color and the qualified thickness of the composite components using the program indicate that the program works well and that this method is feasible for predicting pressurization time during compression molding. The results of tensile and short‐beam shear strength tests show that pressurization time affects the mechanical properties of the final product. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45308.