“What if they do it for 14 days? Does that ruin it?”
Although this comment had sarcastic intent, it hits the nail on the head.
Saying a specific prayer a specific number of times on a specific day by a specific number of people is classic obsessive compulsive behavior. The OCD person is always worried that he didn’t perform the ritual “just right” and will repeat it until done properly.
The practicers of this (and others like it) segulah need professional help.