The mechanical quality of interfaces between polymers is undoubtedly an important player in composite materials research. Consequently, extensive intellectual and financial efforts have been invested in understanding the mechanical aspects (i.e. strength, toughness, etc.) of polymer joints and their implications during mechanical failure of composites. In this work, we discuss the curing time-dependent evolution of interfacial strength in solvent-bonded polymers (identical polymer on either side of the interface) at room temperature. We have found that time-evolution of strength at room temperature is a pure diffusion process instead of the commonly known sub-diffusion process. Consideration of stiffness evolution into the time-evolution of strength, besides toughness evolution, sets the basis for pure diffusion-driven strength evolution. An exponential relation is suitable to describe both strength evolution and saturation at a longer curing time than the typical power-law equation that completely omits strength saturation. A simple dissolution process of polymer samples into solvent material for a different time duration can qualitatively predict the curing time-dependent interfacial strength evolution and saturation for a given polymer-solvent system. Taking this concept of time-evolution of interfacial strength further, we employ varying interface curing time at an interface of a homogeneous bi-layer polymeric system and define a crack deflection criterion based on the interface curing time. We have observed that a mode-I crack propagating perpendicular to the interface prefers interfacial crack-deflection if the interface is cured for less than 45 minutes. The toughness of the bi-layer experiences several degrees of increment due to interfacial crack-deflection. The toughness-enhancement of such a bi-layer system can be significantly altered via modulating interface curing time. Typically, curing an interface for a lower duration of time results in a higher toughness-enhancement.