Rule for omitting duplicates in bruteforce attack?

[undeath]

even if you could cut the time in half (which would be much better than the keyspace reduction you're trying to do), will take a very very long time to run.

Actually, if my math isn't off, it would cut the attack space almost by eight. However, your point still stands. The attack space is way too large.

36! / (36-12)! / 4738381338321616896 ~ 0.127