If CASH is anything to go by which the only PoS coin I've held enough of and long enough to care about PoS, it's not exact.
I've had the coins mint 2-3 days after I expected them too.
Also, there's no coin control feature, so if you've sent any coins, they have gone from the earliest inputs received. Hence, you can only be SURE that the coins received in the first batches are still there for minting.
I'm expecting many posts in the next few days that will be exactly the same as this
lol that is most likely what has happened.. well i'll wait and see i had transactions (received) everyday since launch so one is bound to start..