When to look for investors?

I'm a 1st time entrepreneur who's got a great idea, and being my 1st time, not a lot of clue.

I've developed a proof of concept and have sourced hardware for a prototype and am creating a business plan to flesh out the idea (which as an IT guy is pretty tough going).

my idea is validated by friends saying they know people (and who are people) who have been looking for this specific solution but couldnt find any.

unfortunately for me i cant fund this myself and need to approach others for funding.

my question is, when is a generally accepted good time to get out there to start finding people who would be interested in looking at what i've come up with. If it makes any difference, i'm not in the valley, but in australia.