And here's how we do it: everyone, eat corn. Have a nice corn on the cob, a can of whole kernel corn, or eat whatever variation is best for recognition in your poo. Note the time between ingestion and "Hey! There it is."
And then tell us. Less than 12 hours? 12 to 24 hours? 24 to 48 hours? It will be interesting to see just how much variation there is in the human digestive system.