Could be 5 years, 7 years, 10 years, 15 years, .... maybe never.
Graduating from a school won't make you a chef, it won't even make you a great cook. Exactly what you get out of the school depends on what you put into it, in AND out of class.
In school, you will only learn most of the basics. If and how long it takes to become a chef depends on how much you want it, how much you learn, and if you can find the opportunity. You have to learn to walk before you can increase speed and eventually start running. Its a long grueling process and upon completion of school, you will be starting at the bottom of the barrel, with all the graduates from all over the map.
I strongly recommend you read "Becoming a Chef" by Andrew Dornenburg and Karen Pagehttp://www.becomingachef.com/