If you go to the Quilivant XR website it tells you it as a once a day med that continues working for 12 hours. However some medications don't dissolve properly in XR form so they often don't last as long. I'd rather give the med 30 minutes later and give him a MT Dew at lunch versus increasing the overall dosage. At the rate we are going he will need an increase 4 times a year. He hasn't gained any weight so we will continue to increase a dose that has diminishing returns. We feel the withdrawals are worse than his typical behaviors.
Medicine certainly isn't a miracle cure in this instance.