To test the timer/photocell transformer during daylight hours, you will need to cover the photo eye on the photocell with either the bootie (included) or a piece of black electrical tape in order to simulate darkness.
If functioning properly, it will take up to 2 minutes for the photocell to activate. Do not prematurely assess that the photocell is defective. After waiting a couple of minutes, turn the timer's manual override switch on.