Actually It's already begun apparently. According to Bungie they finished up all the maintenance stuff they had planned for yesterday / today so they've kicked it off early.
At first I was quite interested but now i'm a bit wary of what to expect.
I know one person who has Beta access so I might go around to his place after work and take a look.
Early tweets mention that you might have tears if you try to launch the beta before it's downloaded 100% so keep that in mind if any of you are planning to check it out.
I guess 5 days access is better than 4 when people have real life to deal with but with the game launching in a matter of weeks it feels more like a demo of sorts.