If you're on a Mac and are rather addicted to these sorts of websites, SelfControl (funny name) can be used to block sites for however long you want after some tweaking. I use it when I notice myself opening a new tab in the browser and instinctively going for the "r" or "h" keys.
I too notice that when I block these sorts of websites, even though I still have access on my phone, I start reading a lot more and getting more stuff done. Now that I think about it, I should try the 30 day challenge. The most I've gone is 15 days. Peace out!