V should last 8 to 12 hours and start working within 45 min. If it does not, it would be an indication that the dose is too low. Before trying the Ritalin in the morning, I would talk with your doc about increasing the V one more time.
And yes, you are right that Ritalin is faster working. So it might be worth trying to see how he responds to that. And some people just do better on R anyway. If he does not respond to the R in 15 to 20 min. It may be that he is what Dr. Parker calls a slow metabolizer. See more about that here - http://www.corepsych.com/adhdbook/
Also, I wonder where you got the info that led you to say, " he won't suffer from anxiety that's common from Ritalin since Vyvanse gives a euphoric effect." That is not correct. Anxiety is very common in people with ADHD (over 30%) and is usually helped, not made worse. When V is given correctly it does not give a euphoric effect. It certainly will do that if you do not have ADHD.
Hope this helps. Please ask if you need more info. This will take some trial and error, and I would love to know if you get any answers.