This is more typical than you think, and logical if you think about it.
We assume that are gut transit is really fast, based on the fact we often have to empty our pouch following a meal. But, that is more to do with the gastrocolic reflex of stimulation of peristalsis when you eat, not because what is in your stomach immediately zips right through you.
When you have been fasting all night, things are on the empty side (especially if you have frequent night time stools). Once you start eating during the day, things build up and by the afternoon and evening, things are really coming through.
If you are taking bowel slowers, it is better to try to stay on a regular daily schedule and dose, and wait 4-5 days before fiddling with it. That is because it takes time for a blood level to be reached and the body to acclimate to it. Imodium peaks around 4-5 hours for capsules, and 2-3 hours for liquid. But, its half life is 10-12 hours. So, if you take it regularly, there is a build up over time, until it levels off.
If you are taking fiber supplements or eating a high soluble fiber diet (such as rice), that tends to thicken things, that too can have effects that last longer than you'd think.
So, I guess the main point is to make changes gradually and with one thing at a time. That is the only way you can tell what is working and what is not. If you change things up every day, then it is pretty much shooting blind.
Hope that makes some sort of sense.
Jan