Then why did the payout time on ethermine reduce by ~25% or so ? I get .05 shares every 15 hours instead of the 20 before the fork.
It's the result of Byz fork. Block time 30s -> 14s and block rewards 5ETH -> 3ETH.
It made 15%-20% increase in ethereum mining profit.
There is no increase in profit at all, you are blind to the truth.