This is my next thing I want to trial. Complete block on anything non work related on the laptop. Complete block on anything that doesn't further my values on the phone. But then have an iPad for mucking around and consuming junk content. The idea that it's not easily accessible since the iPad won't be with me at work and it won't be in my pocket being constantly accessible.
I used to have Twitter (my main source of distraction) on my phone and iPad, now I don't have it on any device and it's helped tremendously.
On my computer, I block all distracting sites with the extension I built until noon, then I have 20 minutes for mostly Twitter, then all blocked until 4PM, another 20 min break, and then blocked until 8PM. 8PM-midnight, I do whatever I want. I've found this a fair agreement with myself that I have no reason to break. It created a rhythm for me.
So perhaps if a complete block is too big a stretch, you can give yourself a couple well-defined "fun breaks".
Because the action of checking the feeds or whatever is so ingrained, it's effortless and, more importantly, thoughtless. Even though that extra step is tiny, it can often be just enough of a jolt to make you notice the habit and decide more consciously whether to indulge it this time. After becoming conscious of it more and more, you can choose to break it. Although, in my experience, it's easy for it to come creeping back, too. Once you've destroyed the reflexive nature of it, setting some rules around it can be helpful. And again, even though those rules are just simple, easily-overcome agreements with yourself, they can be enough.