i submitted a preapproved app. for Discover More a few months ago and received the 30 day msg. i too was hesitant to call as it was a bit of a "reach" application for me and to my delight i had been approved.
it won't hurt any less if you wait it out will it? i understand if for whatever reason you'd rather wait but in my case i broke down and called, i couldn't take the suspense 
if you decide to call -you may be happily surprised like i was. i was originally denied for Discover more than a year previous to my more recent app. if your report looks better than it did when you received a denial a few months ago, maybe you'll get the right answer this time. GL!
don't be scared to call them, just dooooooo it 
seriously, even one little mistake that you could have made on the application, like wrong digit input on your social, or address, etc. could automatically make an application go to 30 day message instead of instant response.
good luck
When I applied for the Discover More card last year I received a 30-day reply. A few days later I get a strange call, but didn't bother picking it up. I looked up the number, and when I found out it was Discover, I immediately called them back. It turns out I was approved for a lower 'tier' and I just needed to okay the changes (different APR, etc.).
I would definitely call them. Chances are they just need to verify some information or okay a change like mine had.
Good luck! 
