I think this would vary considerably from person to person, and probably depending on the food (and what other foods were eaten with it, etc). When I had my ileostomy, I pegged my transit time down to about 4 hours, but that isn't really an indicator for problem foods. Right now, not too many specific foods bother me, but if I drink coffee, I'm having liquid BMs as soon as 20 minutes later. I do find other foods increase my frequency, such as yams/sweet potatoes and baked beans, and the effect lasts for as long as 24 hours after I've eaten the food. Other annoyances, like raw green peppers, which cause gas, might start bothering me within an hour or two after eating it. Basically, it's all over the map.
If you are really trying to peg this down, as was suggested to me by my dietician, you should keep a food diary. Keep a list of what foods you eat, how much, and when you eat them, as well as any symptoms you might have (for instance gas, frequency, cramping, diarrhea, butt burn, etc). It's then easier to trace back to a possible problem food, although you may have to chart this for a month or two before you notice any real pattern, especially if you are early out from your takedown. It's not a quick fix.
Also, keep in mind that just because a food has bothered you in the months following your takedown, doesn't mean that it will continue to be a problem. You can reintroduce "suspect" foods again after a few months, perhaps when you start to fall into better rhythm with the pouch. Often you'll find that something that bothered you in the weeks after takedown doesn't bother you as much, if at all anymore.