how long do you let your seed ferment?

[habitat_gardener]

I was at a tomato fermentation demo (at the Sunol Ag Park) last week where the person recommended 3 weeks ("did you say 3 weeks?" I asked. "yes, 3 weeks," he said.) as the fermentation time. (No, it wasn't Fred, it was at another farm.)

I've heard 3-5 days here.

Sometimes I let my seeds ferment longer, though usually not more than a week or so. But 3 weeks?? I'd have thought some of them would sprout by then.