Steam: "available on" date vs "unlock in" countdown

Solution 1:

The Steam client will always show the correct time and date for the release of a game, adjusted to your region. Dragon Age 2 comes out in your area on the 11th of March, which is reflected by the time that the client says it will unlock.

The Steam store does not always show the correct time and date. There have been several games over the past year or so that have seemingly missed their "Release Date" according to the Steam store, but the client reported the correct time and date (to much anguish in the Steam forums). Telltale's "Poker Night at the Inventory" comes to mind here.

Solution 2:

The availability date is when the game is available for download by pre-purchasers. The unlock date is when the game can be played. The extra day is to allow the game to be fully downloaded before playing the first time. Most games that can be pre-purchased can also be downloaded before the release date, although the files are locked until the release date.