Every audience is unique. Is your audience typically available for an 8 am start time or possibly several of the attendees will have to travel a great distance and be subjected to difficult traffic situations which will hinder their arriving in a timely manner? What is the length of the venue? Is it one or two days and is it eight or 12 hours long?
I went to an event which was 7 days long and it started at 8 am and finished at 11 pm every day. Their philosophy was to break people’s resistance down by exhausting them. When someone is very tired, they’re more apt to absorb information and change their behavior. That is an extreme method that is not normally acceptable for corporate event employees. In fact most corporate events are conducted during the week while public events are held over the weekends.
Make sure your speakers plan frequent breaks during the day to prevent your attendees from nodding off. I’ve been to many events that they only allow one hour for lunch but for me to have enough time to check phone and email messages one hour is not enough.