It will be significantly less. I would just set up a recurrence relation for this like so:
A(n) = A(n-1) - C * 2 ^ (N-1) and A(0) = size of keyspace, say 62^12
lets set C = 3.0*10^12 for hashes computed the first year and assume computing power doubles every year.
Plugging this into wolfram alpha yields this function solution for the recurrence relation:
recurrence relation...
f(x) ~= 3.22627x10^21 - 3.0x10^12 * 2^x
Solve f(x) = 0 for x:
x = lg (3.22627x10^21 / 3.0x10^12) where lg is log base 2
x ~= 30.00226 years
Cracked in 30 years, but that's a lot of silicon, no wasted work, and you would need a method to seemlessly integrate new hardware into the running program without stopping it.