How long to regenerate some sperm?

Question

If having intercourses 9 hours apart mean that there is no sperm the second time we had intercourse? Or does it some what regenerate in that amount of time?

Answer

There's always sperm, just not as much in each ejaculation. But to answer your question, it takes 4-6 months for sperm to fully develop.
Regardless, having sex once a day or twice a day shouldn't make a difference with your chances of pregnancy with correct timing

Answer

Fertility endocrinologist suggest wiating 24 hours between ejaculations to achieve best chances. Less than 24 hours and the sperm haven't developed into maturity sperm. Yes it's still possible. But 24 hours between is recommended.