3 or 4 til midday is pretty much my default and I can manage fairly well on it. The problem is any time I overdo it, and my body can consider coffee with friends to be overdoing it, I tend to crash uncontrollably as soon as I'm back in the house, and it's then very difficult to get out of sleeping 6 or 8 til midnight and being exhausted come daylight.

Heat exhaustion is definitely off the cards up here at the top end of the globe, though I actually do better in heat, it's cold that does me in.