some communities set up the Halloween trick or treating hours for a certain day and time, so they supposedly can control what happens to the kids and what they can get up to better, than if they were tricking treating on the actually All Hallow's Night.... I guess they figure if the kids aren't doing it on the night of Samhain, their not doing anything wrong :b ..
well that and some parents don't have the time on the actually day of Halloween to take the kids out, so they get together with an entire neighborhood and make a sorta trick or treat date... if you pay attention to when which neighborhood is doing it, you can literally take you kids out tricker treating every day the week of Halloween