What's interesting is that there are always lines for Confession on Saturday afternoon. On Good Friday, extra hours were added after the service - with all five confessionals - because the lines were so long beforehand. Why we can't have confession in the hour(s) between and before Masses, I don't understand. That's part of the job of priest - to hear confession
At least most parishes have published times. One of the wealthier parishes (I know both of the priests there, too) doesn't even have published times.
This sounds like an opportunity for a crusade....
I've been to churches where they did that, that had multiple priests on staff, but it gets harder to do at churches where there's not a lot of time between masses and only one priest, like ours. But if you ask, he will hear your confession just about any time, without even blinking an eye twice...And he has a whole week at advent and during lent when he's available for five hours a day, beyond the days he schedules penitential services (where he gets four or five priests to come over to hear confessions).
I suspect that it counts on how much the priest feels confession is important, how many people are available to hear confessions, and the mass schedule.