My molasses wash's usually ferment right out within around ten days, depending on weather. Currently the temperatures have been warmish (around 35c) so the time taken is probably a week. I don't fuss about it and just let it go until it's finished. There's no rush.
On the other hand, honey washes take months to finish in the cooler weather, but my latest ferment has been going for three weeks and is still fermenting, by keeping the nutrients up to it. Honey is notoriously slow to ferment out.
So, I guess the answer is that fermentation takes somewhere between a week and several months. If you get impatient the answer is to have - as previously suggested - several ferments going at the same time.
Simple potstiller. Slow, single run.
(50 litre, propane heated pot still. Coil in bucket condenser - No thermometer, No carbon)
The Reading Lounge AND the Rules We Live By should be compulsory reading
Cumudgeon and loving it.