In my experience, these punishments were administered only in pretty extreme situations. As a boy it was in cases where more severe than normal punishment was expected, as a Master, it was even rarer. Cases where a boy would normally be facing expulsion. From my memories, such canings were truly awful. As a Master, when I was called upon to administer them, I tried to make them so. I was acting to avoid the necessity of expelling a boy, and I had to make a deep impression on him, because he was literally on his last chance, if not having really gone past it.
But even with these punishments, boys recovered quickly enough. From memory, they were largely back to normal in less than an hour (although they probably carried marks for a while and might have still been physically uncomfortable, it wasn’t to the degree that it affected how they functioned).