When I have a particularly productive day working on my thesis, I come to a stopping point and just want to shut my computer and move to the next activity. While this is satisfying, it comes back to bite you in the bum.
The next day, when I open my computer, I have a plethora of documents open and datasets and do files without the slightest clue if its saved. I need multiple documents open when synthesizing results, but this system doesn't let you jump back in.
When I sit down to write, I refer to my outline to see what section I'll work on that day. Then I open the corresponding documents and datasets, and get to work. Each day is a different section, particularly depending on a new research idea I jotted down in the middle of the night, if I feel in the mood to write (versus format my endless tables), and who knows what else.
This may sound counter-intuitive, but to keep the momentum going during your next work time, you should successfully 'shut down' your work time when you are done. Not only does it signal to yourself that you completed these tasks you set out to, but now you are free to transition to something else, it provides a clean slate to start back up tomorrow.
Fake it 'til you make it.