I believe all prisoners gets 1/3 automatically knocked off so 20 yrs --> 13-ish yrs for Smyth? That's 3 world cups and a bit.
Not fully correct, a Prison year is 9 months long with good behaviour, that's a Quarter off, not a Third.
(Unless it's a Debt which must be served in full).
Good behaviour meaning not assaulting a prison officer, murdering another inmate or starting a full-scale riot, anything else is acceptable !
But add on temporary release, parole, Etc and most offenders do less than half of what the judges sentence them to.