Hours to solo were never a consideration,
Good job you weren't instructing in the RAAF in my time. You would soon be up in front of the Commanding Officer explaining why you didn't have the confidence or ability to send a student on the first solo within 12 hours max.
Of course if the student was hopeless that is another story and in that case the scrub test would sort him out one way or another. But by hanging on to the student so he can be taught all sorts of nice to know things rather than need to know before things before first solo, is being unfair to your student and an unnecessary financial burden to him. It is command time that will build his confidence - not hours and hours of dual.
There are operators (instructors) in flying schools that think the more dual a student has the better he will be. For that reason they deliberately delay a students first solo for 15-30 hours or more because of perceived "safety".
In reality it is a blatant rip-off. There are new grade 3 instructors who either do not have the confidence to put their student for a CFI check for first solo or worse still want to squeeze a few more bucks out of the student dual and hang on to the poor bastard for as long as possible.