I use it exactly as
@luki7788 said as I compete in classic. If I didn’t though I would likely use on other days as
@b-boy is correct- the best way to bring up a week body part is to work on everything.
In the context of insulin it’s about increasing recovery, utilizing more of the nutrients you consume and the other items mentioned above in the thread.
One thing I would consider first is that you mentioned you’re already on metformin- is this for overall health or because of insulin resistance? I personally would do all I could to reverse any insulin resistance prior to adding insulin.