Welcome to WebmasterWorld Guest from 184.108.40.206
I have seen new pages in the past, targetted within minutes of them being uploaded and viewed.
However the templates I used had the adsense code in already and before I could remove it I had clicked on a number of pages to test my installation.
The ads served were the default charty ones. Within the hour a googlebot (the media partners one) had visited just the pages I had browsed and soon after that the ads where appropriatly page related.
Hope this helps...
But later, 1-2 days, they change and become less so
Are they still targeted though? You could just be experiencing normal ad inventory fluctuations. Also keep in mind that some advertisers turn off their AdWords campaigns over the weekend, if you happen to notice this change from Friday afternoon through Monday morning.
If you are showing PSAs, that is a whole difference scenario though.
If you go to other sites showing AdSense, you will see the ads changing on refresh. Your site isn't being singled out :)