Last month, I attended the American Society for Theatre Research's annual conference. One of the most-attended sessions was on dissertation writing – we added extra chairs and moved to a larger room, and it was still standing room only. Clearly there was a large degree of interest in dissertation writing tips!
One of the recurring themes in the panelists' remarks was that most people write more effectively and efficiently in short spurts. All four panelists stated that two hours was their maximum writing length, and that breaking this up into short segments made them more efficient. Here's an example 2-hour writing schedule:
This works especially for people who normally deal with a lot of distractions – 15 minutes is not a hard amount of time to set aside when you don't check social media, respond to your phone, etc. It also helps reduce some of the physical discomfort that may come from sitting for extended periods of time.
When writing a long-form document like a thesis or dissertation, it's extremely helpful to create a detailed outline before you try to write paragraphs. This will make it very easy to write in short segments, because you'll know what you're going to be writing about next and in how much detail. This allows you to swap out writing blocks with research blocks in case your outline shows that you need to get some more supporting sources.