There's an "old writer's tale" that says the longer an editor takes to respond to your submission, the more likely it is that she is going to accept it. A slight variation of the same tale says that the longer an editor takes to respond to your submission, the more likely it is that she is considering accepting it.
What a crock.
I've spent enough time in enough editorial offices--as an editor and as a freelancer--to know it isn't necessarily true.
Let me describe what happens to the slush pile in the editorial offices of some publications with which I'm familiar:
Publication A: The editor waits until two designated cardboard boxes are filled with slush pile submissions. Then he has a "reading party" and a group of volunteers spends an evening reading the submissions and passing on potentially publishable work to the editor. A submission that went into the box two months ago is no different than one that went into the box two days ago.
Publication B: The editor assigns almost everything to established writers and uses very little unsolicited material. Unsolicited submissions are piled on the corner of the editor's desk until the pile is so tall the submissions start falling to the floor every time he passes. Then he spends an afternoon clearing his desk. A submission tossed onto the corner of his desk two months ago is no different than one tossed there two days ago.
Publication C: The editor has found so little publishable material in the slush pile that he mostly ignores it. Similar to the editor of Publication B, he waits until the pile of unsolicited material interferes with his work, which happens only a couple of times a year. Again, a two-month-old submission is treated no differently than a two-day old submission.
Is there even a glimmer of truth in the "old writer's tale"? Perhaps. At publications where submissions travel upward through a hierarchy of editors where any editor along the way can reject a submission but only one editor can accept it, the length of time before response may indicate potential interest.
But I wouldn't stake my career on it.