It's pretty darn unlikely in our lifetimes. But you'll know about it yourself without anyone needing to tell you before it happens. The energy available to the initial flare and/or associated coronal mass ejection is roughly proportional to the area of the sunspot group.

Before there was a "super" flare and/or CME you'd see the sunspot with your unaided eyes. Check out "The standard flare model in three dimensions. II. Upper limit on solar flare energy" and the figure 4 in particular for size to energy reference. https://arxiv.org/abs/1212.2086

Does this mean the maximum size is roughly an X51?

"Although X is the last letter, there are flares more than 10 times the power of an X1, so X-class flares can go higher than 9. The most powerful flare on record was in 2003, during the last solar maximum. It was so powerful that it overloaded the sensors measuring it. They cut-out at X17, and the flare was later estimated to be about X45. A powerful X-class flare like that can create long lasting radiation storms, which can harm satellites and even give airline passengers, flying near the poles, small radiation doses. X flares also have the potential to create global transmission problems and world-wide blackouts." (1)

(1) https://svs.gsfc.nasa.gov/10109

How much time would elapse from the point of seeing the sunspot until the flare/CME actually occurs?

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.

The odds are 1.

The question is when.

Nitpick: I think you mean that the probability is 1 and the odds infinity.

Hopefully tomorrow so we can stop worrying.

Can we have the Cascadia earthquake as well while we’re at it?

Don't forget the Yellowstone caldera!

What? No love for the ELE asteroid/comet collision?

Cumbre Vieja megatsunami please as well.

Dinosaur killer sized impact vs your volcano. Which tsunami would be bigger? There's more variability in the impact as the volcano is locked to its location, so fun thought exercise for the disaster pr0n types.

Godzilla too?

This thread reminds me of this Calvin and Hobbes comic:

https://thecomicninja.files.wordpress.com/2013/04/calvin-and...

Don't lump me in with that "we."

Yes, within any given year.

That's scary but we can't deny that it will happen.

"O, swear not by the moon, the inconstant moon"

Presumably a reference to: Inconstant Moon by Larry Niven

Worth googling, good short story, and relevant to the "Solar superflares hit Earth" topic.

velut luna, statu variabilis