A wash usually takes between 2 and 10 days to ferment depending on the yeast used, the wash contents and the temperature.
There are a few ways in which you can tell when fermentation has finished.
These are:
1. Measure your SG with a hydrometer, when the SG matches the desired SG for your given recipe and has read that for two consecutive days then fermentation is complete. This is the most accurate way to check if fermentation is complete.
2. Look for fizziness, bubbles rising to the surface: while it’s fermenting there are lots of bubbles coming to the surface.
3. Check the activity in the airlock.