Yes it is a time sink and I can't claim having a specific methodology but if you look at all the conflicting theories, literature and endless blog posts that have been written about validation, you might as well just trust your gut.

My amateurish approach is to jot down every idea in a single line of a text file, then walk away. If the same idea or topic strikes me again, I give it a separate text file and write some copy that might go on the product page, together with links to related stuff, screenshots, etc. Then, after another few weeks and only if I still believe in the idea I come up with more details, perhaps do some light coding, brand ideas, register domains, etc. Then (You guessed it), I wait another few weeks or even months and if it passes my still-relevant check I start working on it on the side of my existing, well, side project. The challenge these days is when to pull the plug or go all-in since the market, interests and attention shifts so quickly that it's tough to adapt without losing temper. Doesn't get easier as you get I older.