An apparatus for determining an overtravel time of a machine, which has a moveable machine part and an optoelectronic protection device, has a light source designed to produce a defined light spot. The protection device for the machine comprises a camera having an observation area in which at least one protection zone having a protection zone boundary is defined. The protection device produces a stop signal when an object enters the protection zone. The light spot simulates an object within the protection zone. The light source is supported by a support element designed to position the light source in the area of the protection zone boundary. An evaluation and control unit of the apparatus is designed to switch on the light source at a defined starting time, and to determine a time interval between the defined starting time and the reception of an “end” signal indicating that the machine part has come to rest.