I seem to remember readng somewhere that 12 hours is just about bang on the expected transit time. But I am no expert.
The article states:
although that figure is a little overstated, because the markers used by the researchers passed more slowly through the stomach than actual food
This study abstract shows the transit time of a telemetric capsule system, however, various foods take longer to go through our systems than others, so it’s hard to say what the average transit time for “food” in general is.
In the above study, the median total transit time for healthy subjects was 27.6 hours with the fastest being 9.6 hours and the slowest 56.4 hours. With there being such a wide variability, tracking your corn is probably a more accurate measure of your own transit time.
I had a friend who insisted that she would pass food several hours after eating it. Like, if she had a salad for lunch she would notice green leafy debris in her turds that night.
I tried to convince her otherwise, but she insisted that what she ate for lunch was actually coming out around bedtime.
I asked her if she ate salads often for lunch and she said, “Yes, almost daily, that’s how I know…why?”.
Never mind.
And seven years for gum! 
This is a fantastic idea - thanks to my little sister. Any gum in the 3 state radius somehow found its way into her mouth (youngest of 8 kids helps, I guess). And it was not unusual to go into the bathroom after her and find (euphemistic) logs that would be 60-80% fluorescent green (or pink or ???). As kids we thought it hilarious (it even came up in code form during her wedding toast by my other sister).
So in addition to corn, I recommend fluorescent chewing gum as an alternative- but you need enough to be able to recognize it later.
Actually, that’s not impossible. But what kind of salads is she eating where she can always recognize it when it comes out the other end?
When I was a teenager, we were telling babysitting stories, and one girl said she had once changed a diaper that was full of speckled poop. She called the contact number and the mother replied, “Oh, I forgot to tell you. I caught her eating some crayons yesterday.”
Wow, full circle. It was right here on these boards where I learned a trick for how to tell which animal in a multi-pet household is eating a particular item: shave a brightly colored crayon into it. Non toxic, and stayes highly visible.
When I had my colonoscopy, I did the clean out the day before and no food for 24 hours. Afterwards I didn’t have to go for almost 3 days, then back to everyday again.
This just out (click bait title but OK cites to academic authors of report; no direct link and I can’t be arsed to find it]
How much do people poo in their lives? *Scientists provide a comprehensive breakdown and the results will surprise you!
Average woman living to 81 will produce an astonishing 25,920lbs (11,757kg)
Due to men typically dying at 76, they create less at around 24,320lbs (11,030kg)
Over a year, the average adult’s stool production weighs more than a panda
In a day, adults create 14oz (400g), which adds up to 6lbs (2.8kg) in a week
Human stool production occurs at a rate of approximately 2cm every second*
Note the two points here about male and female.