I have done slin a couple times off season only and I didn't like it all that much honestly.
I get better gains/pumps with 25mg of Dbol per day.
It has great potential for improving a carbup that is for sure.
Once you have mastered how your body reacts to insulin then you can use it for the wednesday and thursday carbup before a show.
I wouldn't use it on friday or saturday because I know insulin causes water retention and I don't have enough experience in peaking to work around this.
You need to factor in water, amount of carbs, sodium, potassium, diuretics and anything else you may be using on that day.
I wouldn't want to get hypoglycemic on contest day while I am already weak and dehydrated. Recipe for disaster!!!
You can use it while cutting on your carb up day or a little after your workouts.
With GH insulin is more of a neccessity since GH causes insulin ressistance and you need to compensate for that.