Every few days I submit one that doesn’t get a lot of traction but I come back in 2-3 days and it is on the home page, I think these are responsible for maybe 1/3 of my karma but well under 5% of actual submissions. I dunno if these got resubmitted but still attributed to me or if it is part of dang’s “a good submission got missed” program.
Posts that make it to the front page are good for 12-4 hours, I agree.
But if a post gets less than 4 upvotes in the first 15ish minutes, my experience is that 99% of the time it won't get to the front page.