'Time off purgatory' came from a misunderstanding of indulgences, which used to be described in years. So building a chapel could be a 5 year indulgence, a Cathedral, 50 years. The years did not refer to time in purgatory, but to the equivalent time on Earth doing penance.
If you're a big important Lord, you might have killed alot of people, as well as have the means to build a house of beauty and prayer to strengthen the faithful and give God glory. You also may have thought you had too many important things to do, ruling over your turf, to take a penance vacation for decades. So you'd give over your wealth to serve to bring God's love to many people.
I don't know if this system ever worked well, but it certainly was abused, critiqued and finally abandoned. Indulgences are no longer sold.
There are still indulgences, by which I understand them to be the church recognizing particular acts as an opening to God's grace and forgiveness, especially in repentance from sin.