I think the LW was rude and out of line, and so was the kids' mom.
I have, in the past, seen TOTers out as early as 3 - I hoped for the kids that lots of people were home that early!
I would not be surprised in the least if my town has set TOT hours - which I tend to think is a guideline for the safety & convenience of kids, parents, and those with candy to give, rather than a hard & fast rule - but I don't know anything about it, and the city website doesn't mention it.
Quite frankly, I think anything after school on a weekday (or similar time for a weekend) is fair game, but waiting until after-work hours is likely to maximize the fun & the haul for the kids.
I just wish parents would explain to their kids to NOT go up and ring bells at houses whose lights are off. We turned off our front light one year when we ran out of candy and half an hour later our doorbell rang. The dog went nuts and I got to explain to a disappointed teenager that we were out of candy, and any other house with their porch light off should be considered off limits, too. He was mystified.
AFAIK, municipalities setting TOT hours is a relatively recent development - I don't recall hearing of it as a kid, but I do recall one occasion when the city I lived in postponed Halloween for a week - it was very cold that year, and there was ice on the roads, so the city officials put out the word asking everyone to wait a week. A few kids came around on Halloween that year, but not many. Most everybody was OK with postponing.
I do like the towns that give out pumpkin posters (or similar) in the paper or flyers to signify a ToT'ing friendly house- seems like a good way to let families find friendly houses on Hallowe'en, especially if you live somewhere were some folks have become hostile to the custom.
When I lived in a large condo tower, the association put up flyers asking people who welcomed TOTers to register their unit # at the front desk. Then, on Halloween, parents could pick up a list and take their kids to just those units.