I got mine like a week and a half later. You should give them a call to see whats up. Although don't expect much because the office of admissions there is horrible, as you may know.
I never received a little postcard and they said they are processing my application, because i received the secondary by email. I think i should be worried
I think I got U Miami's secondary about 2 or 3 weeks after the postcard, although I was in Boston, so it took a few extra days to get to me. When you do receive it, I think there's a deadline to send it back.
Last year it took 2-3 weeks to get a secondary. But, a secondary is not guaranteed at UM. They send you one only if they like your application. Call them just to make sure. They are starting interviews on September 13, so interview invites for the first 4 Fridays of the application year most probably already went out. Good luck!