The time‐dependent craze failure process of polymers has been investigated. The process is characterized by several stages: deformation, development of microporosity, craze initiation, craze propagation, craze‐crack transition, and propagation of crack to final fracture. Using Laurent’s series expansion and convolution integral form of material’s constitutive function, a time‐, temperature‐, and stress‐dependent instability criterion for viscoelastic media has been considered. It is found that under a constant load, an incubation time for craze initiation can be obtained. This incubation time goes to zero for sufficiently high values of stress and approaches to infinity for low values of stress. The crazing stress depends linearly on temperature, and decreases as the test temperature increases toward the glass transition temperature. The interrelationship among the applied stress, craze initiation time, and temperature is then established and a fairly general time‐dependent theory on craze or quasifracture initiation in viscoelastic media is formulated.