Although Michael's room was close to completion, we delayed finishing the wall with the new window. Eventually, Michael plastered the gaps and framed it in.
I think we both dreaded the sanding of the plaster around the window frame, so that got ignored for several months. However, when Michael was away for a week during June, I decided it was time to get the job done. Kitted out in my Value Village hoodie, I sanded away, covering myself and the vicinity in fine white dust.
Painting the wall and the window frame was easy after that.