Hi,
Download time is aproximately 6 seconds.
Regarding cooling, Sony sensors have a substantially different behaviour from Kodak. While on Kodak sensors you usually have a benefit from cooling as much as you can, on Sony sensors that's really not the case. At 0ºC the sensor already has very good performance, way better than the KAF8300 at the same temp! So, the 460EX doesn't have a deep cooling level, cooling to a stable 25ºC below ambient. But replying to your question, max cooling is achieved within less than 5 minutes.