First Frets currently offers guitar and ukulele courses. (More instruments to come soon!) The first guitar course, Early Essentials, is a primer (hence just 6 lessons or so). It introduces the guitar and covers topics like: learning the parts of the guitar, holding the guitar and holding the pick, tuning, and the overall approach to learning/playing. This course can be digested in one or two days. The remaining guitar courses can take anywhere between one to two semesters each to complete. The ukulele courses, on the other hand, can often be completed sooner, since there is simply not as much material to learn on the ukulele.
As you might assume, the time it takes to complete the bigger guitar or ukulele courses depends on the age and practice habits of each student. A teenager who practices consistently (around 20-30 minutes each day) will complete each course in roughly one semester. (So about 1.5 years to complete the guitar courses, and 1 year to complete the uke courses.) A seven or eight year old, on the other hand, will typically take longer.
I always tell my students to focus on consistency rather than speed or volume. (Be sure to check out This Article to learn about the best practice habit of all time!) Age, natural ability, and schedule vary greatly from student to student, so time to completion will also vary. But every student can develop healthy practice habits that ensure success and enrich the rest of their lives!