If you are just starting out, whether you believe it or not, you already have a set schedule. Even if you say, "I only have school or work from 8:00 am to 3:00 pm, so I'm free afterwards",
You are not.
Whether you are very active or just watch TV for hours at home, you have already set a mental routine that will be hard to remove for you to add a new permanent item. And no, don't ever say the word temporary. When it comes to singing and learning how to sing, there is no such word.
Vocal training can take up from 30 to 60 minutes a day, and while most singers can squeeze some time in the beginning, many start to falter in a few months or weeks. We are talking about daily exercises, or at least daily warm ups. Specific training given by the teacher and rehearsing with songs multiple times. Sometimes this may look like fun, and to a point it is, but above all, it's hard work.
Not all vocal exercises will make you look cool as when you are in the bench press or doing pull ups. Some may even require for you to be alone to work without interruptions or anything that can make you self conscious of how you sound. Some vocal exercises, depending in your needs, will be repetitive and this can tire out even the most focused singers.
But there is no choice if you want to get better. There is no shortcut or magic technique. There is no one exercise that will solve all your problems, and there is no such things as, "sing like the stars in 3 months."
You must work hard not only on doing the exercises right, but self assuring yourself that this training is now part of your way of life, that is normal for you to work on your singing as if you were watching TV or checking your Facebook notifications. It has to be part of you.
Here is a secret: Most students that come to take voice lessons, do pretty good. But that one lesson is not a one time solution. Constant practice is a must and this is where only a handful of students can stay in the race. This is why only so many people get in the most prestigious schools, auditions for musicals or win competitions. Only those who work hard and all the time, will have a taste of glory.
Be one of them.