I'm thinking ahead more to the PSAT than to Halloween. Probably won't go out Trick or Treating because my costume is annoying to move around in, plus I'd rather have a bag of Snickers or Reeses than an assorted amount of candy.
If you plan a big party, haunted house or make your own costumes then it takes more than a couple weeks to get everything ready.
My family does a big haunted house in the yard and it takes a month just to set up the platforms and extra rooms, mostly because the only work times are weekends. On top of that there's decorating. We change the theme yearly so we're always making new props that could take a month or more to make depending on weather and free time. The cattail reeds we harvested for props this year took a week and a half to dry before we could store them.
Costumes can take a week to 2 months to make depending on how elaborate they are and, again, how much time you have to spare for a hobby. Parties generally require having the guests know about it at least a month before the event so people can make sure they can attend, and if it's a party that requires a costume people need time to get around to getting a costume.
Some people put a lot of preparation into holidays, usually because they greatly enjoy them.
I am starting to think about halloween.....I was Snooki from Jersey Shore last year lol I had people come up and take pictures with me..a little to much interaction lol......We never get trick-or-treaters I even tried to pay kids to come here lol but we live in a very rural area and parents take them to the closer retirement type communities..