They may update in 6 to 12 hours, but it all depends on your ISP. I know my ISP used to take 48 hours to propagate, this was irritating, but it appears they are getting better.
On average, it takes anywhere from 12-48 hours for the Registrar, central registry, and ISP to update their records.
The way I usually test it is to use a proxy site of mine which updates immediately so I know when the outside world can see it and my ISP doesnt.