"Problem is that it's virtually impossible to tell what's a good investment until well after the fact. In money as well as in time."

That reminds me of a Will Rogers quote:

"Don't gamble; take all your savings and buy some good stock and hold it till it goes up, then sell it. If it don't go up, don't buy it."

I guess you could rephrase that for time: "Do the best thing you can with your time. If it wasn't a good idea, don't do it."