According to my doctor - after diarrhea, it takes about 5 days for the digestive system to start working properly again (because the bacteria has to build back up to enough). So that would be my recommendation. Have diarrhea and then it doesn’t really matter what you eat after that, the poster would be back home again before they had to worry about pooping.

As someone who has diarrhea anytime I’m going to be in a stressful situation - I can testify that it takes me about a week to “form” poo again.