In the heyday at Meadowlands with 3 million dollar handles, 15,000 people in attendance the races always started on time. Settlemoir tried it for a short time earlier in the year and handle tanked so he weaseled out of it. He didn't give it enough time.
The bettors always adjust and if they know the races are starting on time, they'll adjust accordingly, and after a short time handle won't be affected much.