With the given block time and block rewards, it takes around 11 months or more to produce 500.000 coins (that is the premined coins).
The estimated times calculated with block time is 60 seconds and block rewards is 1 coin per block.
In fact, in earlier phases, block rewards are less than 1 coin, so it will take more than 11 months for sure.
I think that it's too long period.