I am assuming you are asking how long you can let the fermented wash sit before running it?
I always strain my grains from the liquid- so I have the liquid separated from the grains. After fermentation I always try and run my wash within a few weeks. I always make sure the airlock has plenty of water in it and the wash is stored in a cool dark location.
If you have a mash that is fermenting on the grains in a closed fermenter with an airlock I would say you are fine to let it sit a week or two. If you have an open fermenter I would use it soon after fermentation is finished.