I've seen durations of effects with stimulants vary widely in either direction - a handful of individuals obtain benefits for the whole day from a single immediate release dose, and as you describe, some people with long acting forms, where they should be having drug delivered to their brains for hours and hours, feel the effects wear off after just half a day. I think that some of this is attributable to the circadian rhythm that causes a mid-day decrease in alertness (siesta time). https://www.youtube.com/watch?v=hcERA2f2zP8