It all depends on the pussy. It has to be inviting for me to go down. I start every session with the intent of DATY (given it is on the provider's menu). The pussy has to pass the "skunky, stanky" test. Since I always DATY before screwing, I do a visual check and odor check. Unless I get a thumbs up on the freshness test, I probably won't go down.
I had a session years ago where I dined down there for what seemed like hours (probably 20 minutes of real time). She came probably 3 or 4 times. When I was finished, she was so engorged in size (almost 3 times larger than normal) that I really got concerned, but she loved it. We had some great sex afterwards as well. Nothing like getting a lady off.