You should be able to pull off a great name in 1 day. Heroku is a great name: abstracted, unique, interesting and developer related. Ebay is also a great name.
The only reason these names make sense at all is that you already have identified them with a very popular product. That doesn't mean the name is good, it means the product is succeeding despite the name.
That of course raises the entire point of names not being that important overall.
Pinterest, for example is a wonderful name for that company. Microsoft is another. Oracle, even better.
"Abstracted", "unique", and "interesting" are very easy bars to clear when you take "relevant" out of the mix. So yes: I buy that you could come up with a name as good as "Heroku" in a day. Just open up a book of Japanese plant names.
[1]http://www.quora.com/What-does-Heroku-mean/answer/Matt-Van-H...
http://koi-z-are-us.20m.com/japanese_plant_names.htm
... and most of these are viable company names.
One of the things I always suggest to people is running name choices by potential customers when appropriate. As such you simply wouldn't be able to do this in one day. Even if you just wanted to check and see how well people hear the name when you say it and can easily spell it that is going to take some time. The amount of care you take in this area of course is related to what the name is being used for of course.
Heroku is an interesting name and has trademark and brand potential certainly because it's a made up word. The problem is it can be confused spelling wise. You could do hiroku or hirowku or herokoo just to name a few. It's usually a good idea if possible to steer clear of names like this lest you want your email, or some web visitors to end up in the wrong place.
A great name depends on the circumstances. Things have worked for heroku obviously given who they are selling to. It might have been a good name for a car model as well. But I wouldn't say a heroku like name is the right choice in all situations.