As LaRue said, it is different for everybody. In fact, I am unsure whether there are studies that show how long it takes for carbs or any other macronutrient to be stored as fat. What I’ve learned in my general nutrition and exercise nutrition courses is that the fate of carbs will be as such, in the order you see:
1. Broken down into glucose to be used as immediate fuel (only if you are partaking in some kind of physical activity)
2. If the fuel is not needed the glucose will be stored as glycogen in the muscles and liver for future use (how much glycogen is stored depends on how much glucose you used as energy during your last session of physical activity)
3. If the glycogen stores have reached their capacity, it will then be stored as fat
So according to this information, you essentially have “2 chances” before carbs are stored as fat. Let’s hope you did some kind of physical activity before you ate that cake, Casey!