Can you straighten your teeth in 12 months?

Depends. Most orthodontic cases take 18 to 24 months to complete. If it takes a minimal amount of tooth movement to get your teeth straight and your bite is a normal angle class 1, then it can be done in 12 months or maybe less.
Severity/technique. Depends on severity of the problem. Combined dental/skeletal malocclusions require more time. There are some periodontal surgical techniques that when combined with braces can shorten time in rx for adults. Talk to a qualified orthodontic specialist for evaluation of your individual problem and all of the possible solutions.
It's possible. It is possible to have minor corrections done in a year's time frame...The time frame is dependent of the severity of the malocclusion.