Even here inland, where it actually gets hot, I've found that 6:30 is plenty early enough. The heat soaks in here-- it's often the same temperature here at midnight and 7am, only dropping 1-2º just before sunrise. So leaving at 5am would be the same temperature as leaving at 7am, just a lot darker. On the hottest summer days, so long as I'm off the road around 10-10:30am, I don't have to deal with any real heat.