One of the best pieces of advice I ever got about entrepreneurship was from a guest speaker (a seasoned entrepreneur) when I was in school.
When someone asked when was the best time to start a business, he said "never."
He then added that there are always more excuses to NOT start a business than to start one. When you're young, you fear that you don't have enough experience (and no established backup career or resume). Or you have student loans to pay off. When you're older, you have a mortgage and family. When you have a job, you'll find ways to justify why it's better to stay employed. When you're unemployed, you have no capital or income. When the economy is bad, it's hard to get funding. When the economy is great, you're missing out on low hanging fruit (get 'em while it lasts, start business later). There are ALWAYS tons of excuses.
As such, there is never a good time to start a business. You either do it spite of the excuses or circumstances, or you don't. Ultimately, if one decides to do it, it's a leap of faith, which can be impossible for the many risk averse MBAs who like to micro-analyze things to death before taking the next step
Starting your own business is always a risky thing no matter what and it's not about timing or analysis, but purely a gut call - you either do it, or you don't (and there's absolutely nothing wrong if you don't).