Frankly in my personal opinion, its hard. The ground floor is already taken by the investment banks, institutions and major investors as the company prepares to and goes public (IPO).
The time that the market "opens" for smaller investors, the offering is already at the first floor. Not to mention, (not 100% sure, someone clarify), traders with license to trade before the markets open, take away anything thats left between the first and the ground floor.
So, if you are extremely sure the company is going to go up and keep going up, then you could get the shares as early as the market opens. (Unless you are an investment bank or an insitutional holder or a VC, etc., which I assume you are not)
A good point to start could be to take a look at some websites that give a calendar as to when, which company is going public. for e.g. -
http://www.ipohome.com/ http://www.hoovers.com/ Hope that helps !
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