I've been trying out the Harvard Timebox thing, not for side project, but for keeping on top of work tasks. When I remember to fill it out in the morning it works really well. My issues is always setting goals, because really don't care enough about pretty much anything for goals to motivate me. I do know what I need to do in many cases, and writing the steps and tasks down and prioritising them seems to work really really well.
A few articles:
* https://hbr.org/2018/12/how-timeboxing-works-and-why-it-will...
And here is a template here: https://www.docdroid.net/SYMuub7/timebox-template-pdf
On the less practical side: Some of us need peace and quite for a time to become creative. I find that this is increasingly difficult to find in a busy world/life. It's hard to tell other than they need to shut the fuck up for a few hours while your brain reset.