Because it is essentially about changing, enhancing, understanding, building awareness of new physical/functional habits, a frequent and steady pace is preferable at the beginning. This way, the work gets really gratifying for you. Spaced out lessons can be a bit frustrating.
1 hour per week through 4 or 5 weeks, after the one and half hour assessment is a very good way to get started. Sometimes it is enough.
If you have more time, anything is possible. one and a half or two hours sessions are perfect to go from body work to breath and resonance in a same lesson.
If you are not based in NYC, Sophie would be happy to schedule with you, long enough in advance, an intensive program of 1 or 2 hours daily sessions over a few consecutive days. This has proved to be an excellent option.
A workshop is a wonderful opportunity to nail your vocal technique and get long-lasting results in a short time. It is usually designed for a group since it involves Sophie and a pianist accompanist and/or a singing teacher and/or a yoga teacher and/or a Feldenkrais or Alexander practitioner with a perfect knowledge of the use of the voice (other options can be studied).
In any event, this anatomy/physiology based type of work will give you a better knowledge of your voice, its weaknesses as well as its strengths. You will learn how the voice works, and you will get a chance to recognize the physical sensations that will help you install a sustainable technique.