At what stage of my project is the Intrim 800 Series Shadowline door jamb and skirting installed?

They are both installed prior to the plasterboard installation. Door jambs are assembled by forming mitre joints where the head joins the stiles as opposed to the traditional half joint.

The door jamb is then installed and packed plumb and level. It is critical that the jamb material is centrally located over the framing material and runs parallel with the framing material so that the PVC (PLTB 630) plaster stop bead fits neatly against the door jamb material.

Skirting is installed to fit tightly between the door jambs.
The plasterboard sheets are then installed tight against the back face of the 800 Series door jamb and on top of 800 Series skirting.

The PVC (PLTB 630) stop bead is then installed to surround the door jambs. All joints between the bottom edge of plasterboard sheeting and top edge of shadowline skirting are to be plaster set and must also include reinforcing joint paper tape when setting. Also plaster set all PVC stop beads surrounding the door jambs.