Like everything else worth doing, writing takes time. Assembling sentences in your head can take a lot of time. Doing it with the internet sprawling out before you takes way too much time.
So set deadlines, engage website blockers, go for the full Trollope and try to force a certain number of WPM. In the end, you just need to be productive enough to write something great. How long is that supposed to take?
Can you write something great with the rest of #*@!$&* life going on around you?