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?

Thanks for pointing that out. Still, the first 45 blocks are before the cryptocointalk announcement which would make it a minimum of 1.9% premine (17 BTC at 300 satoshi), not the 0.5% premine announced.