The answer to your question, is forever.  There's no guarantee when you'll get the right block answer.  As noted before, you've got an equal chance to solve it in 30 seconds, as you do 10 years from now.  A better question is "How quickly can I mine to get 50 bitcoins if I'm in a pool"  And that comes down to your mhash/second, at 360mhash/sec, which is what my cards are avging out at, I'm doing ~7 bitcoins/month, or just a bit over 7 months to make 50 coins.  You could use that as a rough estimate for how long it would take to get a single block.  As a side note, that dos'nt take into account the tremendous rise in difficulty recently, or how much harder it's going to get to mine.  To be honest, I doubt single miners stand much of a chance, unless you're that guy who wins the lottery every time he goes and plays.