It really depends on how your ADHD effects you. For me, the internet is too big of a distraction, and even when I close everything, I become overpowered. As silly as it sounds, I'll go on the subway from one end of town to the other (a good hour and a half ride) with my laptop and read over notes because I won't have reception on my phone or internet access and so will not be able to be distracted (it also helps that Windows 8 doesn't have the built in games..or maybe I just haven't found them yet). In short, try to get as far away from your distractions as possible rather than just limiting them: it's worked for me!