How long to bake in 13x9 glass pan
Is it just a cake? I don't understand the "cookies" part. If its just a cake, bake it until it springs back to the touch and a skewer inserted in the center (I usually go between the center and the side of the pan) comes out clean.
Can you provide more information? Do the package directions say how long to bake it? Or are you saying you are using a pan of different volume or composition than called for on the box? In any event, as PieceofLayerCake says, generally bake until it springs back when touched lightly in the center and a tester in the center comes out clean (pay attention to the scent of the cake emanating from your oven--it's time to check when it starts to smell fragrant and "ready".