How long does it take before a dog reacts to eating chocolate?

Apparently a plate of chocolate left over from a chocolate pie was left out over night, and I'm worried my dog may have eaten some. She hasn't shown any signs of being sick, but is there any way to know or anything I should look out for?

The level of chocolate that a dog needs to eat to become poisoned depends on the size of the dog and the type of chocolate. White chocolate contains the lowest theobromine level, followed by milk chocolate and then dark chocolate. Baking chocolate contains the highest theobromine levels.A toxic level of theobromine for dogs is between 100 and 150 mg/kg, so a 10-pound dog would have to consume 28 pounds of white chocolate to become poisoned. That same dog would have to eat only about a half-pound of milk chocolate or about 3 ounces of dark chocolate to be poisoned. One ounce, or one square, of baking chocolate would be enough to poison a 10-pound dog. He will vomit or get stomach aches if he has eaten enough of it, keep a eye open and take him to a vet if it continues. You can recognize that your dog has eaten a toxic dose of chocolate from the symptoms. Within the first few hours, the evidence includes vomiting, diarrhea or hyperactivity. As time passes and there's increased absorption of the toxic substance, you'll see an increase in the dog's heart rate, which can cause arrhythmia, restlessness, hyperactivity, muscle twitching, increased urination or excessive panting.

Chocolate is only poisonous to dogs if they have to much.

Your dog would of had to consume a considerable amount. If your dog is 20 lb, your dog would have to consume 5 lb of chocolate (1/4 of body weight) for him to get seriously ill. My dog has eaten chocolate, all kinds and he has not gotten sick. This doesn't mean give him chocolate but that chocolate doesn't always hurt them. *ANYWAYS*... if your dog has eaten 1/4 of it's body weight or something around that, you should see symptoms in as early as an hour or so to up to 24 hours. Some symptoms are throwing up, diarrhea, sluggishness, panting when not needed, hyperness, and loose bowels. Hope it helps