So, how soon will they be back when they realize farming is an order of magnitude more stressful than IT work?

I think that really depends on both the IT role as well as the type and scale of farm. If someone has a really stressful workplace in IT but makes enough money to buy a farm and semi-retire, it could just be that having the farm supplements their food and doesn't need to turn a profit. It's very different to, say, a subsistence farmer or one who has to make a lot to pay for mortgage, retirement, etc.

Honestly when I imagine someone in IT getting into farming, I imagine this. It’s really an acreage with a garden and some animals, but they call it a farm, and aren’t really interested in the actual farms.

That, or they do a hipster-bespoke-organic goat farm, which lasts a few years before they run it into the ground because they’re expecting it to be easy or work like IT. To anyone reading this, I would urge you to explore a significant but less radical change first - there’s plenty of jobs not like coding.