A good rule of thumb at that level is that when you feel comfortable diving within the limits of your current training, then it's time to take that next class. It's always a good idea to get comfortable with what you learned in the last one before signing up for the next one ... that way you'll have the mental and physical bandwidth to concentrate on the new stuff.
When I was teaching, I generally asked my students to log about 20 dives between OW and AOW. Everyone's different, and some entered the class with fewer ... or more ... but I would not accept a student straight out of their OW class. A lot of instructors disagree with me ... but they don't teach the AOW class I did, which included quite a bit of classwork, skills practice, and no "elective" dives.
... Bob (Grateful Diver)
I am on the other end of the spectrum, I believe that you should take the "primary" courses as soon as you can, for example:
Advanced Diver right after the entry level course (Scuba Diver) because:
1. The Advanced Course should condense a dive season's worth of diving into one course. You get to do the diving and skills under the direct supervision of a professional mentor/instructor in much safer circumstances than you learning or doing these skills on your own with a dive buddy who doesn't have the experience or the training to guide you in your learning journey where you may or may not do things right and would be costly if you do it wrong.
2. Avoid picking up bad/unsafe habits or knowledge on the way. Your safest bet is the instructor who is trained and follows a curriculum set by an agency that specializes in delivering knowledge and skills that are safer and appropriate for the diver. Entry level certified students do not have the necessary background or depth of knowledge to judge on what is appropriate skill or procedures on their own especially when they just got certified. The advanced course under the supervision of the instructor must be designed to help the students know their limits with a more realistic scale.
The advanced course I teach includes about 16 hours of classroom time, 10 dives in different conditions including rescue skills, night diving, navigation, buoyancy control enhancement, equipment drills, boat diving, wreck diving, deeper diving, S&R, Environmental orientation, equipment preventive maintenance, etc. with heavy emphasis on proper buoyancy, dive planning, navigation and evaluation and recognition of one's own physical and mental limitations .
First Aid/CPR/Rescue course should follow promptly after the advanced also. Nitrox is either combined with the advanced or should be done on the first opportunity after entry level certification (our dive profile where I am now is most suitable for nitrox).
Other courses I recommend students complete within the first year to two years after certification since they will be needed due to the diving profile in Libya are: Wreck and Deep Diving. My students get 6 - 8 dives per course in these two specialties.