TN visa, how long to get it ?

Hello,

i plan to get a TN Visa in 2008 as a graphic designer but how long does it take between the time i get a job and the time that i can get the visa ?
is it like as simple as cross the border again ? or does it take a procedure etc ?

A citizen of Canada seeking temporary entry as a TN professional under the North American Free Trade Agreement (NAFTA) must submit in person an application for admission at a United States Class A port-of-entry (“POEâ€

thanks for the answer !