I’ll also suggest, with only anecdotal evidence, that going at a certain time might be a learned response, not something from digestion. Somehow I have acquired the habit of going after shaving in the morning, which clearly has nothing to do with digestion. We’ve trained our dogs to go right after they eat. So the brain is not only the best aphrodisiac, it might also be the best laxative. 
There’s also the strange phenomenone whereby many of us find that going to a bookstore is a surefire way to find ourselves with a desperate urge to go number two. I walk into a B&N and within fifteen seconds I have to go to their bathroom.
There was a thread about this a couple of years ago, I think. No one could figure out what could be causing this, even though there are apparently alot of people who have this experience.
-FrL-
Here is some factual information about gastrointestinal transit time
There are instances where transit time is very quick, as in irritable bowel syndrome. The term is called “dumping syndrome.” It’s characterized by a consistant, urgent need to pass stool within an hour of a meal. The stool will contain undigested or partially digested food. The individual will have rapid, sometimes severe weight loss and electrolyte imbalance often requiring hospitalization.
Prolonged constipation can cause a complete bowel obstruction resulting in a ruptured bowel which is a critical medical emergency, often requiring emergency surgery.
IMS, the gastro-colic reflex kicks in about 20 minutes after eating…so the 15 minutes mentioned upthread is spot on.
Drink more water while you’re at it–not caffeinated beverages. Adequate hydration can help soften stool, avoiding constipation. Increase your mobility as well.
Cause it’s hard to spend several hours reading in that position?
There’s virtually no functional difference between squatting and sitting, except the effort involved in squatting is more likely to dissuade you from sitting and straining for hours. Plus there’s a sense of triumph and novelty if you’re not accustomed to squatting, balanced of course by the fear of dumping on your shoes. Having done both I can honestly say that digestively speaking, neither makes for an easier movement than the other.
I understand all the above, I think, but presumably it’s OK to go to the bathroom, when you need to, with a book, do your business comfortably and naturally, and then finish the chapter you’re on with no further, um, activity down below? That doesn’t give you piles, right?
I was under the impression that sitting and leaning forwards with your elbows on your knees somehow contorts your colon in ways that squatting (with the necessary straight back for balance) doesn’t.
Yes, there does appear to be that difference for most people. Standing up and walking around can often produce the same unkinking effect.
It’s extremely easy for contents to get trapped in the folds of the colon. When someone has a barium enema for intestinal x-rays, the gas produced is horrendous. The standard advice is to lie down and roll a quarter turn every few seconds to allow the gas to move past the kinks. This works in the, um, loudest possible way.
The colon, don’t forget, starts in the lower part of the gut and moves first up and then across the body before descending to the rectum. This gives ample opportunity for small blockages.
And don’t get started on the controversy over whether squatting to give birth is more of a natural position. :eek:
I have piles of books all over my house. I read in the bathroom all the time. Are you saying there’s not a connection? 
I think- and I’m not joking- that it has to do with the excitement of entering a big shiny warehouse full of books, CDs, and magazines- excitement can sometimes = needing to crap, and fresh rows of books = exciting.
It also probably has to do with the, similar to what’s been talked about, pre-programming we’ve done to ourselves: we enter a B&N, and we know we’ll be there a while, so our body tells us to hit the bathroom. Makes perfect sense- hitting the bathroom allows us optimum time spent in B&N after the bathroom.
It’s something a lot of people say, really without anything to back it up except for the fact that a lot of people say it. All I can say is try it yourself (a “dry run” is sufficient") and observe your body position to see if it is really dramatically different.
My personal experience is that there’s no significant difference in the overall quality of execution. In fact, if things are a little slow, the squatting position seems to generate even more pressure that I consider to be unnatural and uncomfortable.
Among people who are regularly faced with the squatting vs sitting dilemma, it can generate pages and pages of debate, so really it’s about what works best for you. However I have never seen anybody cite any medical proof that one may be better than the other.