Obs Cop
Like you i work shift, mine is 4on 4 off, and I tried to do the IR on my days off. I had a 2 hour drive to Stapleford round the M25 before each lesson and even allowing for a tea break on arrival found myself not doing as well as I'd hoped in the sim.
I found that by returning to work/family life for four days I was just not retaining sufficient knowledge from week to week, this was exasperating for the instructors as well as myself as we had to go back over stuff that I felt I had mastered the previous week. Also, the guys who stayed on site, were able to back seat or front RH seat other peoples sessions. This is an essential part of the training in my opinion as when the pressure is off you, you are able to observe other peoples mistakes and formulate your own plans for avoiding those same mistakes.
Faced with the seemingly inflexible deadline of my exam passes expiring I decided to terminate my course after 10 hours as I knew I would not be ready for test on time. It was a difficult choice to make.
Now I am thinking of re-taking the relevant exams and redoing the IR, but I will only do a full time course wherever I decide to go.
Best of luck !