I speak from over 30 years as a buyer. I would like to see sellers accept Early Birds rather than state definitely no early birds. Sometimes if I can get to some sales early, it means I can fit more in. Also, given the time the sun rises this time of year, I think all your sellers should advertise 6.00 am starts.
The buyers are on the road before then, and in my experience almost all sellers I meet will open well before their advertised time.
Sellers should all be made aware of the fact that they only get one chance with a buyer, and buyers will not come back if sent away.
Also, I never go to garage sales where the street number has been left out. I don't have time to drive up and down the street waiting for some sign to go out. These sellers miss the boat almost entirely.
If people arrive early prepared to buy, why not let them in? The early birds are out early prepared to buy and they have more sites to go to. They don't want to be sitting around waiting.