This could be anything from one or two classes to several years of college.
Most adults enrolled in technical colleges also work.
At community and vocational schools, many classes are offered at times that can fit into a busy lifestyle. There's lots of support and services for returning adults. More and more classes are also being offered in distance learning environments such as this one. If you already have a college degree or have equivalent professional career experience, take a look at Advanced Technical Certificates. They are generally 9-12 credits in advance training.