When I upgraded mine in January 2009, the free month started after the trial time had ended. Also, the subscription plan I added didn't kick in until both the trial period and free month were finished.
Every in-game benefit I've seen so far (such as lifting the trial restrictions, or getting booster pack powers) has taken effect within a few minutes at most. Make sure you're logged out of the game while you apply the new serial code to your account. It wouldn't hurt to give it five or ten minutes before you log in again either, especially if the store just released something new.
Welcome to the game! Hope you decide to stick around 
As Triplash stated, the restirctions should be lifted immediately, and the time is ADDED to your current "play until" date listed on your NCsoft Account management page.
Thanks for letting me know! I wasn't sure if I should wait or not glad to know that I don't have to!
..>And thank you for the welcome ^^
I currently have until the 21st for my trial...
Does anybody know if I were to upgrade my account tomorrow would it just immediately go to the free 30 days or would it start after the 21st?
And if it does wait until the 21st to add the 30 days.. do I still have my trial restrictions until then or do I get the restrictions removed right away?