I agree with both of you -- the morning and afternoon meals can stimulate defecation within 10-30 minutes. But not always. What's coming out, is what they ate 6-10 hours earlier, depending. We tracked this carefully for a month. Here's the pattern for 10-15 week old puppy, fed three times a day:
Wakes at 4:30 or 5:30, poos and pees (no meal). Back to sleep for an hour or two.
Feed at 6-6:30 am, may poo again within an hour, but definitely will poo in 6-8 hours, around noon -1 pm. Noon meal may stimulate that.
Following noon meal, will defecate around 6-7 pm. Evening meal at 6-7 may stimulate that, may not.
BUT, feed at 7, won't poo until 4:30-5:30 am.
As he ages, all this will change of course. As an adult, will eat twice a day, and after evening meal at 6 pm, won't defecate for 12 hours or more.
Peeing is a different story altogether. Peeing happens all day long. As others have stated, it's crucial to take out after waking from naps, after 5-10 minutes of intense activity, and of course, just after eating (to encourage timely defecation too).
We use a bell inside and that helps a lot. At first he used it mosly for #2. But now for a week he's been using it for #1 too and is getting consistent. He hasn't peed in the house for a week. SO SO happy about that!!!