Today morning, Blizzard reduced the cooldown period for characters that have already undergone a paid character transfer from six months to one month.
"This will allow players who have already transferred their characters to then move to a different realm after one month if they so choose, to meet up with friends, or just join a different realm community. If you have transferred your character already and are past the one month mark you can now transfer it again if you choose to do so through the Account Management page."
You can find the full post on the official World of Warcraft forums.

http://www.curse-gaming.com/en/