If/when you build up a tolerance it will take a very long time for it to build up (as opposed to adderall, which is an amphetamine) just because of the way the drug is. if you've just started taking them, you should be more worried about potential side effects than a tolerance building. however, i've noticed that on the first day of taking a new med its like a fair bit more effective than it during the following days, so don't expect it to be as awesome as the first time you took it.
also side note getting high on ritalin/focalin kinda fucking sucks i get bad stomach cramps and its a really weird high if you're trying to get high look for better options