I don't believe in parole or time off for good behavior. If your given 20 years, you should do twenty years. If you "misbehave" and break the rules, you do 30 days on bread and water in solitary, with the 30 days added to your 20 years.
When I was in the service, if you went to the brig, each day in the brig was added to your enlistment time. I had a guy come into my squad in Viet Nam that already had 3 1/2 years in on a 3 year enlistment, and had 13 months to do in Viet Nam. He was making up his "bad" time.
I think that's exactly how it should be. Why should someone get rewarded for good behavior in jail? This after they've murdered or raped. It's immoral and wrong.