With 'normal' sentencing a prisoner is automatically released on licence half way through the sentence if the sentence is one of less than 4 years. If the sentence is one of 4 years or more he can apply for release at the half way stage but it's not automatic. If he's refused he can periodically reapply for release up until two thirds of the way through the sentence, when he's then released automatically on licence. The licence period ends in all cases at the end of the nominal sentence passed by the Court.
However 'extended sentencing' (as in the case Hc4361 refers to) works differently. When an extended sentence is passed the chance of release at the half way stage disappears. The offender will remain in prison up until at least two thirds of the way through the sentence but can't actually be released until the very end of the sentence without the consent of the Parole Board.
If the normal licensing period applied that would mean that the offender in this case could be released after 16 years (with 8 years on licence) or, say, 20 years (with 4 years on licence) or after the full 24 year term (with no licence period whatsoever). However the judge has ordered that the licence period will be fixed at 8 years, irrespective of the time served in prison.
https://www.sentencingcouncil.org.uk/about-sentencing/types-of-sentence/extended-sentences/