I personally treat it like more of a last resort.
If there's a chance anything can get better, if there's something in process, if life is turning around in any kind of way, I'll delay it and earnestly try my best to keep going despite the thoughts. Because at the very least, if it's turning around even in a small way, that's still progress. That's something to be happy about. When things start nosediving it's back in the cards, just in the back of the deck so I can give myself a chance to think it out and for life to show me a sign.
Even if a few things fail, it's still worth not slapping on a due date for yourself to me. I think it's worth giving life a chance, it's not like there's anything to lose by not doing so. Your guidelines don't need to be strict.
For me personally, the day I CTB will be when I have none of those few things left and haven't made any new ones in a while. I don't wanna rot, I want to die happy and beautiful. It's nice to know that I don't have to suffer through all of it once I'm exhausted and alone, i don't have to rot, I can just drift away and it won't hurt anymore. But until I finally run out or the pain becomes unbearable, I think it's worth the struggle.