When it comes to submissions, the slowest are essentially open-ended, because you will find magazines that never get back to you. I once sent a story to Weird Tales and never heard back at all. I've had one story THAT WAS ULTIMATELY PUBLISHED take a year to get a response on. (I had crossed it off my submissions log.)
I DO have a new record for the fastest response - last night I sent a story to Neo-Opsis (a new market for me) at about 11 p.m. I found the rejection in my e-mail when I got to work at 8 a.m.
I've had some electronic rejections take as little as 24 hours in the past, but this is a record!
I went to the post office this afternoon and bought some IRCs (they had to order them especially for me). The next story I send to Neo-Opsis is going postal. Reject that overnight! HAH!