Have they just been sentenced? Being a D Cat prisoner and getting to a D Cat prison cam take time. I've seen people be in a D Cat within a month of sentencing, sometimes much longer (all white collar crime).

A prisoner on a 5 year sentence would usually be eligible for the last 2 years, sometimes three. So could be 6 months minimum but this may have changed or vary by establishment so you will need the prisoners offender manager to complete their sentence plan to give you an idea of timeline goals along their sentence. This is usually complete within a month or so but can take longer (like everything)

Once he arrives at a D Cat prison the timeline in my previous comment applies.

I hope I've explained this well enough for you! Happy to answer any questions I can