Haven't been around chickens much since I was a kid on the farm. As I recall they weren't the brightest bulbs in the barnyard.
Attached is a schematic for my concept on how to control the door. The photo cell controls a relay that is shown in the up position during the day and the down position during the night. The door (or motor) has two limit switches, one for up and one for down. As can be seen, when the Photo Cell relay changes states, the motor will be energized to move the door until the appropriate limit switch opens and stops the motor.
The motor can be powered by the mains or whatever power source is appropriate. Reasons to use a battery are, if you want it to work if the main power fails, or for safety. If you power from the mains, your must be careful to insulate all connections to the limits switches, etc. so no lethal voltages are exposed.
Also, you would want to have some way to easily open or close the door manually if needed (perhaps a quick release connection for the actuator rod).
The photocell could be the kind they sell in many hardware stores to control outside lights.
For the door actuation you could use a motor with a gearbox reduction which drives a wheel or crank with a diameter equal to the distance you want the door to move and with a connecting rod to the door. Thus the wheel/crank moves 1/2 revolution to open or close the door and always moves in one direction.
The limit switches can microswitches positioned to sense the door or motor crank position.
I don't see any need for a timer. For safety you may want some sort of IR beam sensor which would detect anything in the door opening and stop the motor. Perhaps something similar to the sensors they sell to detect when someone goes through a door at a business.
You probably also should have some method of protecting the motor if the door jams. Perhaps some type of slip clutch or motor overload protector.
So building all this should be a good test for your handiness. Have fun.
P.S. Let us know how the chickens like it after it's built.