I don't know if I'd place it solely in the "broscience" category. I mean you're right about the fact that 30 min is not like magic time, but if that is a consistent time you can take it, and most people will remember it right afterwards as opposed to 3 hrs later. Also, people that are consistent about scheduling their nutrition and workouts, tend to be the ones that see results. One of those "correlation does not indicate causation" kind of deals.
However, if it works for you, broscience or not, why not stick to it?