In any good voice acting training program, the number of lessons you will need to be prepared for entering the marketplace and producing your demo(s) will depend on the degree of competence you demonstrate in the evaluation, assuming that your basic talent is there. If you pass the evaluation and move on to voice acting coaching, it is assumed that you have the ability to overcome the problem areas revealed in the evaluation session.
This is different for everyone. People come to the table with a variety of problems. Some pronounce certain words incorrectly. Others have a weak background in English grammar and don’t understand certain aspects of language dynamics. Still others have a tendency to rush their delivery, or aren’t engaged in the meaning of the script, or don’t end their sentences with strength and emotional power. These are just a handful of the potential issues. Everyone has these problems, to a greater or lesser degree. Some have more. Others have fewer.
Therefore, the answer to how many lessons you will need is as many as it takes to get you to the point where you are capable of doing work that is well-received in the marketplace. So it is up to the judgment of your voice over coach to make that determination.
A word of advice here: Don’t sign up for a program that offers a package of a fixed number of classes or lessons and a demo. This is a one-size-fits-all approach, and it absolutely won’t work, unless you are already an accomplished actor or public speaker.
I am also not a believer in voice over online classes or in-person classes for beginners. To learn how to do voice acting effectively, you need to work with a voice acting coach on a large number of scripts to learn to master the challenges of as many subject and mood categories as possible. One-on-one voice over training is the only way to accomplish this in a reasonable length of time.
Most of my students need at least 24 lessons at a minimum. Some have worked with me for a year or more. The number of lessons required is also affected by the number of demos a student wants to have me produce, since each category introduces hurdles of its own.
The best way to keep the number of lessons down is to practice diligently, be very attentive in the lessons, and set about learning everything you can about the voice over marketplace.