The announcement was made at 19:03:00 UTC (UNIX time 1399230180).

The first 12 blocks totalled 1.5 million coins, which is 0.5% of the total 300 million coins, so that is the advertised premine.

But actually, the first 56 blocks have timestamps earlier than the announcement time (example: block 56 has timestamp 1399230110, i.e. more than one minute before announcement).

And if you assume it takes people a minute or two to download wallets, setup miners, get synced up etc, that is approximately 60 blocks pre-mined.

As the first 50 blocks have extra high rewards, the premine calculations would be:

 - 56 blocks is 6.85 million, i.e. 2.3% premine
 - 60 blocks is 7.25 million, i.e. 2.4% premine

Before I use bold red letters and the 'S' word, can someone please check I'm not missing something stupid?