There is a lot more in singing than you imagine.
The duration of the course varies from person to person based on their potential.
You will get to learn all the right singing methods to come out of your wrong singing methods.
If you think you are a good singer but would like to seek professional guidance to grow as a professional then you need to take up voice culture technique courses. Voice culture technique is an art to make your voice sound sweet in all the three octaves of your vocal range. It mainly involves art of breathing, usage of the right voice, handling of micro and macro dynamics, syllable strength training, usage of microphone techniques for singing on stage and studio, improvement of the overall gain of the voice and the psychological fitness to handle any situation during performance.