I second what boonez123 and aeden said, that was indeed wise advise.
In addition, I would say, as soon as you see a need (but, validated through market research, formal or informal) go after it. There are lots of intelligent people thinking out there, who are as capable as seeing market needs as you or me or the next person. The only thing that matters in these days of open source and low cost startups is execution - who comes first to the market with the better product.
A need that is not met can be a current $0 dollar idea but if developed well can be a future million dollar idea. If you hit on a million dollar idea when you are poor, thats how you would get rich!
Before/during/after college? - 'Now' would be best.