A valve timing adjusting system comprising: a displacement mechanism unit (31, 32) that displaces a rotational phase of a camshaft relative to a crankshaft of an internal combustion engine between a retard position and an advance position, a locking mechanism unit that locks the rotational phase at an intermediate locked phase positioned within a displacement range of the rotational phase by inserting a locking pin into a locking recess, a hydraulic pathway having a hydraulic control valve that hydraulically drives the displacement mechanism unit (31, 32) and the locking mechanism unit, and a control unit having a control system that controls operations of the hydraulic control valve, a lock release process that releases the locking of the locking mechanism unit completes the locking release by supplying oil pressure to the locking mechanism unit for moving the rotational phase from the intermediate locked phase toward one of the retard position and the advance position, and then supplying oil pressure to the locking mechanism unit for moving the rotational phase toward the other of the retard position and the advance position; the rotational phase is caused to stand by at a predetermined position of the one of the retard position and the advance position past the intermediate locked phase during the lock release process, until a standby time has elapsed; characterized in that the control unit includes a property obtainment unit that obtains property information regarding hydraulic properties of the hydraulic pathway, the property information including a rotational displacement change rate (λ) that is computed based on a change in an actual rotational phase of the camshaft relative to the crankshaft; the system further comprises a standby time changing unit that changes the standby time based on the property information. a displacement mechanism unit (31, 32) that displaces a rotational phase of a camshaft relative to a crankshaft of an internal combustion engine between a retard position and an advance position, a locking mechanism unit that locks the rotational phase at an intermediate locked phase positioned within a displacement range of the rotational phase by inserting a locking pin into a locking recess, a hydraulic pathway having a hydraulic control valve that hydraulically drives the displacement mechanism unit (31, 32) and the locking mechanism unit, and a control unit having a control system that controls operations of the hydraulic control valve, a lock release process that releases the locking of the locking mechanism unit completes the locking release by supplying oil pressure to the locking mechanism unit for moving the rotational phase from the intermediate locked phase toward one of the retard position and the advance position, and then supplying oil pressure to the locking mechanism unit for moving the rotational phase toward the other of the retard position and the advance position; the rotational phase is caused to stand by at a predetermined position of the one of the retard position and the advance position past the intermediate locked phase during the lock release process, until a standby time has elapsed; characterized in that the control unit includes a property obtainment unit that obtains property information regarding hydraulic properties of the hydraulic pathway, the property information including a rotational displacement change rate (λ) that is computed based on a change in an actual rotational phase of the camshaft relative to the crankshaft; the system further comprises a standby time changing unit that changes the standby time based on the property information.