How many open water dives are required for SSI OW certification?
The book work is "home work." A 10 year old half wit could complete the book and KR's on his own in 10-ish hours. The teaching part is making sure the student understands the subjects covered in the KR's, and that they understand the subjects covered in the quizzes/exam. Why would an instructor need to be involved in the "home work?"
DD's schedule above is similar to the norm all over the warm water world;
If the students make prior arrange they should be told it is best to complete the book work before getting on the plane; many attempt to do it on the plane. To really make a good start to the class the first three chapters/KR's need to be completed before sitting down with the instructor.
Another 3 day option is start with the Intro Dive. Then you decide you want to be certified, so you get the book and do the first three chapters/KR's before the next session with the instructor. That next session starts with reviewing the 1-3 KR's and quizzes, then as much of the confined water as possible, but at least the first three CW sessions; then you can make OW Dive 2. Third day with the instructor is the remaining KR's, quiz and exam, remaining CW sessions and remaining 2 OW Dives.
Or you could do all the remaining CW work the second day and third day just chapter 4-5 KR's, quiz, exam and 2-4 OW training dives.
The vast majority of certified divers in the world started by booking a 3 day course; mentally and physically challenged prospects might not maintain the pace to complete in 3 days.