Started the flush this week. It felt like the right time. I've got significant nute deficiency in the upper leaves of the main cola now. What is surprising is that since taking away all nutes, several of the buds have shown new growth. I was going to flush for just 4 days as its a DWC, but having seen quite a lot of new growth, I'll probably just leave it a few days longer and see what happens. Checking the plant several times a day now, so it's being very closely monitored.