Why do the boys postpone their treasure hunt to Saturday? 44

The boys postpone their treasure hunt until Saturday because Friday is unlucky.

“Lookyhere, Tom, do you know what day it is?”
Tom mentally ran over the days of the week, and then quickly lifted his eyes with a startled look in them—
“My! I never once thought of it, Huck!”
“Well, I didn’t neither, but all at once it popped onto me that it was Friday.”
“Blame it, a body can’t be too careful, Huck. We might ’a’ got into an awful scrape, tackling such a thing on a Friday.”
“Might! Better say we would! There’s some lucky days, maybe, but Friday ain’t.”