It really depends on the effectiveness of your practice. At the end of the day, singing isn't just about playing the right notes. How long does it take to learn to sing? Exactly ten months and three days. If you think it sounds weird, you're right.
Some people are born with very little vocal ability, while others are naturally gifted singers. But everyone, from the shyest shower singers to the professionals, can always learn more about singing. Going from a basic level to an intermediate level of singing takes six months to a year of constant practice. As with other sports, constant repetition develops muscle memory.
Basketball players run drills at every practice. They run laps to gain endurance and practice all kinds of coordination exercises. It will depend on how much work you do in it and if you have any previous experience, but you can definitely learn to sing in less than 6 months. Then move on, as you can continue to improve and develop your vocal technique.
That said, you can speed up this process by simply practicing more. The 3-year rule for me is a singer who practices 1 hour a day at least 5 days a week. If you practice two hours a day, you can speed up this process tremendously. It all depends on how much you want it and your willingness to spend time.
Tuning and tuning problems can often take a few months to correct;. But I usually advise people that it could take 6 months or more to notice a clear difference. All you need to benefit from voice lessons is an open mind, diligence to practice and a love of singing. If you're not sure what difference there is, this video describes how trained and natural singing voices differ.
Once you train your voice to sing with the correct technique, your muscles will begin to remember how you taught them to work to create a specific sound. If you work with a singing teacher without exams, and you don't need to work as a singer, it will take several years of weekly classes before your voice is considered “trained”. They spend a lot of time training and singing scales, practicing phrasing, analyzing lyrics and finding a balance between a solid vocal line, phrasing and emotional distillation of the musical pieces they perform. As we have seen, it may take a while to master singing or to become an expert at it, but with some of the helpful tips above we can make a lot of changes very quickly to our voices.
The only thing that a voice teacher can truly offer a student is to give the student a solid framework to train themselves to acquire skills to operate their vocal mechanism as efficiently as possible, as well as musical knowledge and artistic understanding and appreciation of singing and performance. With the help of your teacher, you identify that the reason you don't have free and easy high notes is because you're too heavy at the bottom of your voice, so your vocal cords separate (the flipping) and your larynx rises as you rise in tone (the possible squeeze). The voice is one of those instruments in which simply laying the foundations is such a task that most people never get to that point. Having a trained voice means that you have been taught to sing with a correct, and sometimes specific, technique.
Each of them has trained hard and continues to train, and will probably do so for the rest of their careers.