Ya know, I disagree with this advice. Give it a couple of hours tops. If you don't enjoy the process after a couple of hours and the goal is a whole day away, you won't get there.

Give it three minutes tops. If you cant focus it doesn’t matter that you might enjoy it.

/sarcasm :)

Whether to give it a month or three years depends on the ambition of the goal and the things learned in the process.

The point is a little deeper than that. You might finish 10 to 20 different 3+ year projects which means almost nothing makes that cut. However, you can likely do 500+ one month projects. The second one is much closer to the number of interesting projects you might come up with in a lifetime and a month is long enough to see some real results on most things.

Spend 100+ hours learning to juggle over a month and you’re not doing tricks, but you’re going to be noticeably better at it. 3 years on the other hand is a long way from say mastering French, but it’s plenty to be useful on a trip. And that IMO is what separates two benchmarks, noticeable improvement is rarely worth much on it’s own.