The immediate release form of ritalin has an expected half life of 1.5 – 4 hours on average. Meaning that about 50% of the medication will have expended its effectiveness and been eliminated from your body plasma. Only my opinion but a more effective regimen may be an extended release in the morning and an immediate release later in the afternoon. I might add that we have not experienced very good results with this medication. The most important thing to remember is not to give up or get discouraged, this is a journey and eventually you will find your sweet spot. I would refer you to the posts from ferret and remember that not all problems in narcolepsy patients are improved by pharmaceuticals.
All my best