I'm up at 5am for work too. How much sleep do you need? Mind you, I'm only 4 or 5 minutes drive from the track!!
The early evening start time gives families a chance to do something during the morning/afternoon and get to see some speedway too. A mid afternoon start could put some off, especially during warmer weather. On the other hand, many NL meeting go on for ever due to numerous falls. We'll be lucky if we're out of there before 8pm, too late for those with very young children who have to travel far.