For both of your cases, the "25 to 30 minutes task" trick won't work at all. For a case that persists for years, what I've learned is that it's either real ADHD, or some emotional problem around the topic. For me, it was 100% an emotional problem, though I do have a bit of a scattered mind, but I can focus it, whereas I've seen people with serious ADHD who can't do it at all and need meds (among other things).
For example, having many interests is fine, but when it comes to choice, what keeps you stuck can be something like a complete fear of regretting the choice. Words like lazyness or perfectionism are usually the sheep's clothing that the wolf (emotion) is wearing. How can some organizational trick from a blog post help here?
I've read lots of self-help books (among other things) when I faced these issues a few years ago, and there's a curious commonality: it's all small tricks developed for the author's personal experience. But what I've noticed is that there are two kinds of people in these situations: the ones who don't a solution and get out of the problem (which is the group that happens to include most of those authors), and the ones who stay stuck looking for an answer, a quick solution, a trick to escape.
The first type can get out by using something like the GTD book. That means their problem really was that they lacked some crucial bit of organizational knowledge to unlock their path towards whatever they want to do.
But the latter type (the ones who're stuck in the cycle) need to let something go rather than accumulate new things (in this case, tips and tricks about Getting Things Done).
There's the DIY path (hard, involves journaling, introspection, noticing and categorizing your emotions, reading Jung, reading ancient texts like the Bhagavad Gita) and the psychologist path (you need to find a good paychologist who doesn't just ask "and what do you feel about it?" over and over but actually takes an active role in your situation and your circumstances)