I bought one for about £120, it doesnt have the timer but does have the light sensor.
It does close the door at a reasonable light in the evening after adjusting the sensor and I have never found any of ours still out when I finally get round to going down in the evening and double checking and closing the run door. I have also checked it when its really cloudy and it doesnt shut them out.
Best money I ever spent, there is nothing worse than getting caught out in the evening somewhere and knowing your chicken are not safe and away. Dont think of as much as the primary system of locking them in - just a great secondary failsafe, if, for whatever reason you forget or cant make it.
They are very expensive for what appears not very much high tech electronics, but it does have some clever bits in there to automatically stop the gate if it gets stuck, resets and retrys again without burning the motor out, stops automatically at the top and the bottom and the battery last for years.
Plus they are easy to fit, just get a jigsaw, a drill and a screwdriver.
I did think about making some lever device that would only operate the door if all the choock were sat on it - but then I realised it wasnt the great egg race and I was no Professor Heinz Wolff
Ta
Baz