IMO, it's pretty simple. If you aren't welcoming TOT'ers on Halloween night, turn off your porch light, bring your pumpkin inside and don't answer the door. (Or if it's daylight and the porch light wouldn't be on anyway, just don't answer the door). I think 5 PM is just a tad early and a bit odd to do it during daylight hours; people are just getting home from work and probably aren't ready yet; it's traditionally an evening activity. When I was a kid, the much younger kids started at maybe 6 at the very earliest; older kids would go maybe 7 to 8.
(I have never heard of set TOT hours. Who decides and enforces this?)
Depending on where you live, 5 pm can be dusk, if not all the way dark. If you are on the eastern edge of a time zone, sunset is just about an hour earlier than if you are on the western edge of the same time zone.
My town has decided, along with several others in my state, to hold TOT on Tuesday night*, instead of Wednesday. There's a few towns in my state that have made the official TOT date Saturday or Sunday. (Please don't ask me why; I haven't a clue.)
No one really enforces this--if someone knocks on my door at 4:30, I'm not calling the police. I think the set hours are to spare people from getting random knocks on the door at 10 pm or later. The different dates? I'll have candy ready on Tuesday (or whatever date they decide will be the hurricane rain date) and only that day. Someone could go out another day, but I doubt they'd get any candy.
*Which is the day Hurricane Sandy, or it's remnants, will be descending on us, so who knows what will happen?