Adderall XR vacation - break from drug?

I am currently prescribed (2) 30 mg ADDERALL (adderrall) XR pills / day. I have been taking them fairly steady for about 10 - 11 months. The drug works great for me and really helps me be the person I need to be. It really unlocked my creativity and intelligence at work and has vastly improved my life. Recently, the drug has been losing its effectiveness. I will have an opportunity in the month of July to take some time off of the drug. I have a full week without work, but I could try to not take it during some work days as well. My questions is, typically (and I know it varies with people) how long does it take for a drug holiday to affect tolerance? I just want to make sure 1-3 weeks will help and that I am not wasting my time. I doubt I would be able to take any longer than that off with out it affecting my work performance. Any help is appreciated.