Your dump cake is ready when the top is set and golden brown and the edges are set. The center will be wobbly. Meaning that when you nudge your cake, the filling should be firmer around the edges but still jiggle in the center. If in doubt, insert a knife into the edge of the filling; if it comes out moist but clean, it's ready. It doesn’t have to be bone dry right out of the oven—remember, the filling continues to set as it cools.