In Texas, it has to be 6 hours, there's a mandatory test, mandatory videos, and they seed classes with inspectors to make sure the instructors are doing their job (it also has a mandatory minimum cost leading to courses that come with a free movie ticket, free tanning, free buffet, etc...). At the end of the class, you have to sign a statement that the class was 6 hours long; if you lie, you can go to jail.