Most are 1 year...12 months. Some as little as 9 months (don't know if I would be comfortable with that) and as much as 18 months (if 18 months, it would make more sense to go for the ADN and have the RN credentials.
I totally agree with Dixiedi. I believe that Platt College in Tulsa has an LPN program of 18 months. I don't know if that's the path designed for PT students or not. However, if you're going to school for that long, it makes sense to possibly get your RN. And ADN program lasts for 2 years. Just my .02.