I don't know how it works exactly, but I have a family member that has been sentenced to multiple years... twice actually. On both occurrences, after just 30 and 90 days I got a phone call., "I'm Out. Come Pick me up." You don't have to be a celebrity or have connections to get special treatment. Just luck.
I imagine too, there are probably rules for early release... like non violent crimes, past record etc. Maybe we have a lawyer in here who can tell us.
P.S. This was 8+ Years ago and my family member has mended his ways. #NoJudgement