I bred X. borealis several years ago. The eggs were laid on 4 July and the newly-metamorphosed froglets were vocalising just 12 weeks later on 26 September. I never observed amplexus though. The vocalisation occurred during a feeding frenzy or when a frog got unwelcomely close to another. The vocalisation appeared to signal that the frog doing the calling wanted the other frog, or frogs, to back off rather than it having anything to do with mating.

I have though, observed a young male Hymenochirus frog clasping another frog only 6 weeks after metamorphosis, which was surprising.