I get 10.8 years
600gh is 0.006341 btc a day according to bitcoinwisdom
I divided that into 25 coins and get 3942.595 divide by 365 = about 10.8
and about 3942 to 1 on any given day. with our current diff rate..
problem with these estimates is they are base on current diff rate.
the rate dropped more then 2% last adjustment so you have better odds this adjustment then the last.
our adjustments have been good lately.
so good I run this at a solo pool
http://solo.ckpool.org/users/1JdC6Xg3ajT3rge3FgPNSYYFpmf53Vbtjemy cost is 7 cents a day to run the 117gh at a solo block my odds are 22,222 to hit a block so with 'normal luck'
I will spend 1555.54 usd to hit a block currently a block is worth 5625 usd.
unfortunately I can't scale up to large hash rates with my location.