I agree, the amount of time you spend can really vary. If you're going after a space with major incumbents, it should be much longer, because you really need to drill into the strengths, weaknesses, and opportunities of your competitors.

I reference CrunchBase and AngelList not because it's only startup-startup competition, but it's a great place to look for new entrants that you often won't find through Google alone. If there are major incumbents in your space, you should find them with that initial google search.