A time-dependent analytical model for capacitive sheath is developed for describing collisional radio-frequency sheath driven by two sinusoidal sources. In this model, it has been assumed that ion motion and velocity are time varying and sheath is collisional. The time-dependent terms in ion-fluid equations are ignored. Based on the assumption of steplike electron density profile model, analytical expressions for instantaneous sheath motion and sheath potential have been developed. The plasma-sheath motion and sheath potential are compared with a time-dependent model for collisionless and a time-independent model for collisional capacitively coupled plasma.