Some species, such as Drosophila pachea, require weeks for an adult fly to become sexually mature, while in others, such as Drosophila mettleri, either sex can be ready to mate within hours of emerging from the pupa case
It's interesting how different species have such drastic differences in their mating habits, I would think that the species that can mate the earliest and most often would survive due to the potential to create more organisms faster, but different strategies emerge that work in their own way.