A valve opening/closing timing control apparatus and method can be used with a camshaft whose rotation is synchronized with opening/closing timing of an intake valve or an exhaust valve in an internal combustion engine; a relative rotation angle adjustment mechanism which transmits torque of a crankshaft in the internal combustion engine to the camshaft and which adjusts a relative rotation angle between the crankshaft and the camshaft; and a lock mechanism which depends on hydraulic fluid, and which mechanically locks or unlocks the relative rotation angle that is adjusted by the relative rotation angle adjustment mechanism. The apparatus and method determine the duration of a time period from a start of the internal combustion engine until a start of relative rotation angle adjustment, based upon an unlocking force of the hydraulic fluid that is applied to the lock mechanism when the lock mechanism is locked and the internal combustion engine is started.