How long does it take for ritalin (methylphenidate) to affect focus? 30 minutes? 1 hour?

Ususally 20-30 min. Depends a bit on the specific type of methylphenidate you are taking, but most of the oral forms begin working withing 20-30 minutes. How long the benefits last will depend again on the form you are using and the dose, as well as how your body handles the medication. Effects can be as short as 2 hours for regular immediate-release Ritalin to 10-12 hours or more for some of the long-acting kinds.