If you refer to the avatar of the OP..................then i must say you got a good taste ;-)
Back on topic
The preview is available as soon as MS releases it, dates are given but are not 100% exact, but probably somewhere at the end of next week.
The Official carrier updates depents on your carrier and device so a exact date cant be given.
Some users just got the Blackupdate, if you see what i mean.
And at Manoj..................Yes all WP8 devices and that includes the 520.
They have already showed a 520 with wp8.1 on the last weeks event.
But please use the search opt, or look in the Lumia 520 section of the forum.