It’s increasingly common to take it for T1s, and things are commonly prescribed for “off label” (non-FDA approved) use all the time.
I take metformin ER, 1000mg 2x a day (worked up from 500 1x a day initially). In my case, it was actually my endo’s idea. It is awesome—I went from about 23u of basal a day to 16u with improved control and markedly less dawn phenomenon. I also lost about 13 lbs and have kept it off, returning to my usual weight that had crept up over about 4 years before I started it (suggesting I was developing some insulin resistance in addition to the T1).
Definitely ask for the ER formulation. Time of day absolutely does matter, and while I would ask start on 500mg 1/day to see how it does with your GI tract (some people have a lot of side effects; some like myself do not), I might suggest trying to go to 2x a day for more even coverage.