I'll let others help you on the how-long-does-it-take, but you really might want to use the card pretty soon. Citi likes to see its cards used (so they told me), and it would be a shame if they closed it for lack of activity.
As the other poster said, that courtesy credit might well have been a gentle nudge from citi to get you to start using it again. (I'm not a citi fan; I'm just cursed with one of their cards that I'm trying to get some GW on...)
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007