As you noticed, not only do weekends offer a significantly improved chance of making it to the front page, but also: the mid-morning weekday peak seems to cause enough competition that submissions have a hard time making it.
This is in contradiction to an assertion made in the OP: "Your odds are slightly better when submitting at peak activity (weekdays at 12 PM EST / 9 AM PST)." The problem being, they did not calculate the odds.
As you noticed, not only do weekends offer a significantly improved chance of making it to the front page, but also: the mid-morning weekday peak seems to cause enough competition that submissions have a hard time making it.
This is in contradiction to an assertion made in the OP: "Your odds are slightly better when submitting at peak activity (weekdays at 12 PM EST / 9 AM PST)." The problem being, they did not calculate the odds.