Hard to say. For a "super" event the sunspot group might be noticibly big right after it appears and flare during the emergence which would mean a ~day or two warning all the way up to a long established group slowly growing over an entire rotation around the sun and coming back to flare and/or erupt ~29 days later.

So, does that mean we'd have time to shut off our power grid and disconnect any long lines of metal?

AIUI, it's only a problem if sufficiently long wires are actually connected to vulnerable equipment.

Yes. But I think there'd be a lot of political/social problems with that. The solution for the grid at least is to spend the infrastructure money to put fast ground fault interrupters on all irreplacable (<months) big backbone transformers.