I recently disabled an img on DT wanted to delete it as it has been designated for another project. Although the image is out of public view, they still "hold onto it" in what they told me was "liability reasons" or something like that "for a couple of months". No specific timeframe was given to me.
On FP, I have been doing some gallery cleanup there. Deletion takes about 1-3 days, and it's just simply gone after the request, no holding in any of their queues.