I agree that an instamine isn't exactly the same as a premine but when 35% of the outstanding coins were created in one day that is highly significant. I'm not sure that one day gap really makes that big a difference compared to just issuing 35% of the coins in the genesis block. It's certainly worth noting somehow anyway.
By that definition, practically every PoS coin out there was "instamined". Most are 100% mined within a week.
Not if that was the published distribution schedule. Fast, yes. Dumb, maybe, but not an instamine.
Dash did not adhere to the published schedule. At all. First of all the difficulty didn't adjust properly due to a (alleged) bug. Second of all the number of coins created was too high due to a (alleged) bug (and the extra coins were not returned the way they were with Bitcoin). Third of all, the future rewards were arbitrarily lowered after the instamine.
That does not apply to "practically every" anything, other than "practically every" instamine scam.